better test

fix fluid_benchmark.py

* add flatten op

* enable dist se resnext

* small batch size

* refine regularization for selected_rows

* clean lookup_table

* refine rpc_server_test

* temporally disable rpc_server_test

* fix rpc_server_test

* add unit test

* update test_pe_mnist threshold

* clean code

* Hiden some LoDTensor ralatted ops' Python wrapper.

* hide variable API

* edit API.spec

* expose rank_loss python api

* get diff for all changes in current branch

* diff with upstream/develop

* let dist test serial

* Fix serious bug in nesterov momentum optimizer.

* wip add se-resnext test for 2x2 and parallel exe

* testing

* finish dist unitest 2x2

* update python interp

* fix gpu number

* make this test can run in parallel

* Fix Reduce and Gather

* Fix unit test

fix AUC op
optimize it's test

* remove block api

* remove clone_variable

* hide block inner apis

* update

* fix tests

* fix auc

* update

* update

* fix compile

* fix param name

* add doc string

* fix test

* Add learning rate decay test

* fix test name

* doesn't share @LR_DECAY_COUNTER@