Improve trainer API

Refine distribute transpiler api

* "fix double type error"

* "fix ci"

* "softmax fp64"

* "fix momentum"

* "fix ci"

Make Variable support for future.division.

Fix grpc server ready condition

* Fix the bug when a input variable of op is dispensable.

* Add HasInputs/Outputs interfaces to OperatorBase.

* Remove the unreferenced header file.

Clean cross entropy

* Initial implementation of forward pass for MKLDNN batch norm

* Added attributes for MKLDNN batch norm

* MKLDNN batch norm forward pass passes unittest. Started working on backward

* Backward pass for MKLDNN batch norm added

* MKLDNN batch norm: scoring added to forward pass

* MKLDNN batch norm: bias as input added; handling AnyLayout when kernel is looked up

* MKLDNN batch norm: python unit tests added; mkldnn tests removed

* MKLDNN batch norm: changes required by cpplint

* MKLDNN batch norm: refactoring the operator

* MKLDNN batch norm: saved variance inversed in backward pass for correct execution of MKLDNN unit tests

* MKLDNN batch norm: refctoring, function for static/const cast to void* added

* MKLDNN batch norm: remove AnyLayout from batch norm

*  MKLDNN batch norm: only NCHW format is supported. Unittests refactored

* MKDNN batch norm: use_mkldnn added to attributes

* MKLDNN batch norm: AnyLayout removed from unittest

* MKLDNN batch norm: added CUDNN defines to batch norm

* MKLDNN batch norm: undefined data_format variable corrected

* MKLDNN batch norm: use_cudnn added, use of setUp method for configuring attributes

* MKLDNN batch norm: added use_cudnn attribute to batch norm operator

* MKLDNN batch norm: correcting batch norm unit tests for MKLDNN

* MKLDNN batch norm: MKLDNN tests moved to another file; reverting changes for saved variance not being inverted

* Change default layout to NCHW

* MKLDNN batch norm: init_kernel_type method added to unit tests

* MKLDNN batch norm: style changes

* MKLDNN batch norm: unit tests refactored

* MKLDNN batch norm: added use_mkldnn attribute to batch norm python interface

* fix __shfl_down_sync_ of cross_entropy

* use reduceSum

* "fix ci"

- The trainer and inferencer will load params from disk if param_path
  argument is not None in their constructor.

- Remove params.py, we will expose core.Scope to the user if needed
  (e.g., for GAN). Currently we will not expose it, unless we clearly
  know doing so can support GAN.

- Add `save_params` to Trainer (a TODO item).

- rename "network" to "program"

A naive implement trainer.train by executor

add some instructions for running vgg distributedly

Merge branch 'feature/add_stable_test_of_cross_entropy' of github.com:reyoung/Paddle into feature/add_stable_test_of_cross_entropy

Fix cpplint format check

Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into feature/add_stable_test_of_cross_entropy

* "fix double type error"

* "fix ci"

Use multi thread to do update

add lookup_sparse_table_op

Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into fix_grpc_server_ready_condition

* Fix cpplint issues in sequence_padding

* Fix typo in cu file

* Fix dependencies of sequence_padding

* Add include

* Fix CPPLint issues in fluid/inference/tensorrt/

* Fix compile errors

Fix unittests

Merge branch 'develop' of https://github.com/PaddlePaddle/Paddle into fix_grpc_server_ready_condition

install ccache in Dockerfile to speed up compile