Discover new tests in run_tests.py (#64246)
Summary:
Introduce `discover_tests` function that globs for all Python files
starting with `test_` in test folder excluding subfolders which are
executed differently
Fixes https://github.com/pytorch/pytorch/issues/64178
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64246
Reviewed By: walterddr, seemethere
Differential Revision: D30661652
Pulled By: malfet
fbshipit-source-id: a52e78ec717b6846add267579dd8d9ae75326bf9
