uniform logger manager in FleetAPI.
hidde API under distributed/utils which users don't need.

* fix bugs of reducer

* update

* update

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* refactor mp in eager mode

* update

* update

* add uts

* remove unrequired ut cases

* update

* fix bugs

* update

* support process group in dp with fleet api

* update

* fix uts

* update

* add uts for EagerReducer

* add more uts

* fix bugs

* fix bugs

* modify

* modify uts

* fix bugs

* update

* update

* update

* solve conflicts and merge

* add some other uts

* modify time of uts

* update

* update

* update

* remove uts of resnet

* fix bug

* fix bug

* refactor reducer

* modify cmakelists

* solve conflicts

* rename group and update process_group

* fix bugs of ProcessGroupNCCL

* modify for CIs

* refactoring reducer

* Add solutions to PyLayer which is unsupported in DataParallel

* modify note format for parallel.py

* modify docs of dataparallel

* add docs of dp with pylayer

* modify docs format

* modify example format

* change example of dp with pylayer

* add unittest for dp with pylayer

* modify ut

* merge latest codes

* update

* modify for CI-Coverage

* modify text-indent

* dygraph sharding

* update unitest hybrid_parallel_communicate_group

* fix pipeline

* fix mp pp dp

* fix utest of hybrid parallel

* add utest for tuple

* support control flow

* supoort sync_parameters_buffers

* fix the bug of sparse embedding