* 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

* optimize rank_attention, test=develop

* use the paddle memory pool, test=develop

* set max size, test=develop

* limit the max size, test=develop

* fix the head of cu, test=develop

* add AsDispensable, test=develop