optimize pyreader

* fix selected_rows bug
test=develop

* refine cos_sim
test=develop

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fix mac

Delete buggy selected_rows functor

test=develop

add vadd, vaddrelu jitcode

fix run error on mac

test=develop

test=develop

recordio is not the official API in Fluid 1.0. Remove unittests for it.

test=develop

`cwd` was not set before when get commit SHA. The default `cwd` is the current build directory. However, the build directory might not be the subdirectory of source. The `git` command will fail when that happened.

test=develop

Dry run tests will skip `Op.Run` and just perform job scheduling. It helps to analysis dead lock in PE.

test=develop

test=develop

refine analysis_resnet50_tester

clean rpc server profiler

test=develop

Fix googlenet bug with rule

fix_recordio_internal_link

test=develop

*  fix mkdir conflict

test=develop

Optimize thread pool

test=develop

* add fp16 backward support
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* add sum_op fp16 test

* disable test_dist_save_load
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* add check_grad for sum

* add unit test for softmax_grad fp16
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* add scale_op unit test

* add mul_grad_op unit test for fp16

* add cross_entropy_grad and eman_grad unit test for fp16
test=develop

* fix cross_entropy unit test

* add pool2d fp16 unit test

* refine conv2d fp16 unit test
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* refine activation unit test
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* fix ci
test=develop

* follow zhihong's comment, copy from https://github.com/PaddlePaddle/Paddle/pull/12796
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Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into optimize-pserver-profiler-thread-pool

test=develop

test=develop

Revert " Exhaustive search for cuDNN conv."

This reverts commit ce7d9b07.

* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Clean code
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.

test=develop

Fix rmsprop_op enforce bug

test=develop