The fixed APIs:
6 Methods in paddle.fluid.io.PyReader
paddle.fluid.layers.Preprocessor
paddle.fluid.layers.py_reader
paddle.fluid.io.save_params
paddle.fluid.io.save_persistables

test=develop
test=document_preview

* update some op doc, test=develop

* remove nccl dep when the number of GPU is 1
test=develop

* fix dygraph mem leak, test=develop

* polish msg, test=develop

test=develop

fix role_maker bug
test=develop

* fix py_reader iterable bug, test=develop

* move data from buffered_reader,test=develop

add paddle cloud role maker for customized usage, note this is only for industrial users that have cloud environment pre-configuration (#18121)

add paddle cloud role maker for specific cloud usage. This pr will simplifies user's configuration in distributed training.

* Update backward.py:
     - If there is no input grad var in all outputs of previous ops, do not append this op into graph.
     - Only apply this stragety when double backward.
* Update some double backward op.
* Update sum_op to judge whether a tensor is empty by numel or IsInitialized().

test=develop

* test=develop
add detection output for supporting retinanet

* test=develop
add test_layers.py

* test=develop
add API.spec

* test=develop
alter test_retinanet_detection_output.py

* test=develop
alter round 2

* test=develop
alter retinanet_detection_output

* test=develop
alter paddle/fluid/API.spec

* test=devlop
alter detection.py

* test=develop
alter retinanet_detection_output

* test=develop
alter paddle/fluid/API.spec

* test=develop
alter detection.py

* test=develop
alter API.spec

* test=develop
alter retinanet_detection_output

* test=develop
alter paddle/fluid/API.spec

* test=develop
alter python/paddle/fluid/tests/unittests/test_retinanet_detection_output.py

* test=develop
alter python/paddle/fluid/tests/unittests/test_retinanet_detection_output.py

* test=develop
fix grammer error

* test=develop
fix grammer error

* test=develop
fix grammer error

* test=develop
alter python/paddle/fluid/tests/unittests/test_layers.py

* test=develop
alter paddle/fluid/API.spec

* add class name and timeline for test_dist_base.py

* test=develop
add sigmoid_focal_loss for supporting retinanet

* test=develop
add test_layers

* test=develop
add API.spc

* test=develop
alter sigmoid_focal_loss_op.cc

* test=develop
alter detection.py

* test=develop
alter API.spec

* test=develop
alter round 1

* test=develop
alter simooid_focal_loss

* test=develop
alter sigmoid_focal_loss_op.cc

* test=develop
alter test_layers.py

* test=develop
alter paddle/fluid/API.spec

* test=develop
alter sigmoid_focal_loss_op.cu

* test=develop
alter paddle/fluid/operators/detection/sigmoid_focal_loss_op.cc

* Update generate_proposal_labels_op to support CascadeRCNN.

* test=develop add target assign for retinanet

* test=develop
run ci

* test=developp
add test_layers

* test=develop
add APi.spec

* test=develop
alter round 1

* test=develop
alter rpn_target_assign_op.cc

* test=develop
alter test_rpn_target_assign_op.py

* test=develop
alter rpn_target_assign_op.cc

* test=develop

alter API.spec

* test=develop
alter paddle/fluid/operators/detection/rpn_target_assign_op.cc

* test=develop
alter rpn_target_assign_op.cc

* test=develop
alter python/paddle/fluid/layers/detection.py

* test=develop
alter paddle/fluid/API.spec

* fix code bug
test=develop

* fix get items slice bug; test=develop

* fix unique_name bug; test=develop

* add print log for unittest of distributed training
test=develop

* Remove layers.detection_map API
* Since uers can use fluid.metrics.DetectionMAP to calculate mAP of current-batch and cumulative-batch. layers.detection_map only can calculate cur-batch mAP.

test=develop

* update CPU_NUM config
test=develop

* added unit test for QAT FP32 & INT8 comparison

test=develop

* enabled other models and updated filenames

test=develop

* added accuracy check and multiple batch handling

test=develop

* removed quantization_mkldnn_pass.py

test=develop

* cleanup

test=develop

* updated model paths

test=develop

* renamed tests without MKL-DNN

test=develop

* fix reusing mkldnn pool2d primitive

test=develop

* add performance measuring

test=develop

* fix accuracy statistics

test=develop

* removed non-mkldnn tests

test=develop

* added conv2d_depthwise->conv2d mkldnn transformation

test=develop

* format update

test=develop

* fixed creating key for pool2d grad

test=develop

* added pass

* Fix the accuracy issue while using float precision to get the scale.

test=develop

* Fix the format issue when 'X' is not nchw.

test=develop

* removed output comparing and changed number of images

test=develop

* cmake and comment fix

test=develop

* updated acc threshold for QAT comparison tests

test=develop

* added OMP_NUM_THREADS setting

test=develop

* enable all QAT INT8 tests

test=develop

* restored upstream version of a file

test=develop

* modified directory names

test=develop

test=develop

* fix save/load in Fleet
* add UT framework of Fleet

* Fix the GetExpectedKernelType of add_position_encoding_op.
test=develop

* Fix the doc of lstm_unit outputs in nn.py.
test=develop

* support avx and noavx core

* add catch and give some log

test=develop

* fix build

test=develop

* add missing package

test=develop

* fix pybind name

test=develop

* fix import error

test=develop

* conbime noavx core

test=develop

* add requirements

test=develop

* fix unkown message

test=develop

* fix api spec

test=develop

* refine and clean

test=develop

* update

* pass dist ut

* follow comments

test=develop

* refine scripts

test=develop

* test=develop
The scatter op has a calc bug when the indices has same index, the scatter op use overwrite mode to calculate the same index, fix this bug by using the accumulate mode to calculate the same index.At the same time, the gather op has the same bug when the op calc the grad. And we use the lib of open-blas and eigen to optimize the time cost in accumulate mode.

* test=develop
Fix some code format problem, and the same time add the test case in gather and scatter op

* Cherry-pick fix random Python3 CI failure.

In some tests, SWEs used "print('xxx').format('xxx')". The syntax
is only supported in Python2, not python3. However, since those
lines are related to data download, if the CI machines already have
the data, it passes CI tests. That causes random failure.

* Cherry-pick: disable CUDNN case of test_warpctc_op

Also temporary disable a unit test. The test will be fixed under high priority.

* fix im2sequence padding bug, test=develop

* fix edit_distance, test=develop

* add API.spec,test=develop

* fix logging unable. test=develop

* unset sys.stdout for stream handler. test=develop

* fix newly add basicConfig. test=develop

* fix import error. test=develop

* add shape not match doc to data layer, test=develop

* fix API.spec md5
test=develop

* add deformable psroi pooling

* test=develop

* test=develop

* test=develop
modify format

* fix bug

* test=develop run ci

* test=develop
add API.spec

* add test_layers.py

* run ci again

* test=develop
run ci again

* run ci again

* test=develop
run ci again

* test=develop
run ci again

* test=develop
run ci again

* add space between two lines

* test=develop
add space between two lines

* test=develop
add space between lines

* test=develop
modify comment in nn.py

* test=develop
add space between two lines

* test=develop
add space between two lines

* update API.spec

* run ci again

* test=develop
run ci again

* rerun ci

* test=develop
rerun ci

* change input shape

* run ci

* test=develop
run ci

* modify format of nn.py

* test=develop

* test=develop

* test=develop
update API.spec

* test=develop
fix API doc

* modify API comment

* modift API comment

* test=develop
update API.spec

* test=develop
modify comment

* test=develop
modift comment

* test=develop
modift comment

* test=develop
update API.spec

* test=develop
modify comment

* test=develop
add inference in nn.py

* test=develop
update API.spec

* test=develop
resolve confict

* test=develop
update API.spec

* add unfold op
test=develop

* fix divide bug in python3 when calculating output width and height
test=develop

* add name=None in python api, move redundant code into inline function

* try to trigger ci for this code
test=develop