* 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

* add white list for dist passes

* update comment

* follow zhiqiu's comment

* fix PassContext attrs type

* add split_program

* make ut faster

* increase ut timeout

* make result deterministic

* add fuse_all_reduce pass

* add ut framework, update

* fix ut framework

* remove useless code

* add coverage support

* update

* fix CI

* fix some bugs and fix ci coverage

* fix conflict