This reverts commit 29f1560d.

* Support python3.8

test=notest

* Fix install pr requirements.txt

* test=document_fix

* Add details to the summary and test it, test=document_fix

* Add set +e before example, test=document_fix

* Remove test code, test=document_fix

* Optimize summary information and test it, test=document_fix

* Remove test code, test=document_fix

* Restore file changes caused by pre-commit and test it, test=document_fix

* Change argument of checkout, test=document_fix

* Remove test code, test=document_fix

* add retry on mac

* fix some error

* fix with some errors

* Show more possible problems with build_and_check in file paddle_build.sh, test=develop

* Remove test codes modified in file device.py for build_and_check, test=document_fix

* Fix missing blank space in file device.py, test=document_fix

* Final process via summary_check_problems function, test=document_fix

* Add the option to execute unit tests only at night

* set ut nightly label for 3 cases.

* add unittest for paddlerolemaker with gloo

* Fix inference bug

* fix inference lib

* add fleetrun command for distributed running; test=develop

* add ci check for changing op-related api without core.ops, test=develop

* generate api_source_md5 file when build, test=develop

* add failed example, test=develop

* add failed example, test=develop

* handle exception, test=develop

* add reinforcement learning model test=develop

* align backward test=develop

* add gym in paddle_build.sh test=develop

* rm pip install in script test=develop

* refine paddle_build.sh test=develop

* fix sed error in macOS test=develop

* polish code test=develop