* 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 env value to  log to stdout; 2.Add logger name

* Optimize log messages in dygraph-to-static

* Replace logging.warn and warnings.warn with logging_utils.warn

[Dy2Stat-debugging] Fix bug: Returns True if the verbosity level set by the user is greater than or equal to the log level (#26858)

* [Dy2Stat] Add debugging and logging mechanism for dygraph to static. 

* Remove TransformerError temporarily. 

* import mock in PY2, from unittest import mock in PY3. test=develop

* Expose interfaces set_code_level and set_verbosity in paddle.jit, fix doc of the two interface. 

* polish doc of set_verbosity and set_code_level.