* 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

* fix pslib. test=develop

* add device to train_from_dataset. test=develop

* refine fleet.stop_worker. test=develop

* fix ut. test=develop

* fix ut. test=develop

* fix executor & ut. test=develop

* fix executor & ut. test=develop

* fix executor & ut. test=develop

* [iscan] bugfix

* test_standalone_executor modify

* upgrade comment string to raw string

* fix string in

* fix string with ' '

* revert update on comments

* upgrade only necessary

* fix sample code checker

* fix comments with '''

Integrated Trainer of Parameter Server (API add `fluid.contrib.layers.sparse_embedding` only) (#22957)

* Integrated Trainer of Parameter Server

* remove async executor python api
test=develop

* remove test_async_executor.py
add executor train_from_dataset demo
test=develop

* fix import bug
test=develop

test=develop

test=develop

test=develop

test=develop