* 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

* refactor check_pr_approval, allow using github login-id

2. remove the tricks for paddle.fluid.layers.ops.func

* add testcases

* simplify the test data, and added to file diff approvals

* remove a approver

* test_print_signatrues runs on a simple pipeline, no paddle installed

* testcases for print_signatrures and sampcd . python3 only.

* remove unused import directives

* remove unused import directives