* 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

* [Eager] fix sharding under eager mode

* [Eager] fix several sharding test under eager mode

* Recover using _test_eager_guard

* Ensured fleet.init under legacy

* Ensured fleet.init under legacy

* Fix CI issue, re-definition strategy and call fleet.init() in stage2_offload

* Modified dygraph_group_sharded_api.py, move fleet.init to a better line