* refine to_string

* re-enable ut

* add xpu test

* notest;add kunlun_test

* notest;add kunlun_test

* notest;test=kunlun

* notest;test=kunlun

* notest;test=kunlun

* notest;test=kunlun

* test=kunlun

* add gloo initializer, test=develop

* add gloo initializer, test=develop

* try to fix paddle save load test

* open paddle save load

* replace dataloader

* remove dataloader

* add op_function_generator.exe retry in windows, test=develop

* modify test_imperative_using_non_zero_gpu from use two gpus to one gpu, test=develop

* remove objgraph

* remove graphviz

* fix ut

* Use the single GPU card to execute the test_fuse_bn_act_pass UT.

* parameter_server_optimizer support auto_strategy

* refine launch and distributed repr string for print

* add auto parallel L1 implementation
test=develop

* fix fluid.embedding

* Add RNN related apis in paddl.nn
test=develop

* new rnn api, cell almost done

* add new progresses in rnn APIs for 2.0

* refine rnn APIs and docstrings.

* add unittets

* disable gpu tests when paddle is not compiled with cuda support

* remove unnecessary imports

* fix docstring

* add to no_sample wlist

* backport to python2 to avoid yield from

* add **kwargs, fix typos

* update docstrings for birnn

* rename argument for SimpleRNN and SimpleRNNCell, fix sample code

* add default value for initial_states in fluid.layers.birnn
Co-authored-by: Nguosheng <guosheng@baidu.com>

* add TensorDataset. test=develop

add collective op for cpu using gloo and paddle.distributed.* apis

* find timeout unittests

* setting timeout value

* fix some error

* fix some error

* fix some error

* fix no newline of end file error

* consider the combination of different strategies to work together

disable test_dist_fleet_ctr

* disable UT temp

* add save/load for parameter server