Clean up raise exception logic (#55656)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55656
### For release notes
What:
- All errors that are silenced by "raise_exception=False" are now GradcheckError (which inherits from RuntimeError).
Why:
- Due to a refactor of gradcheck
Workaround:
- If you catch for 'RuntimeError' with `except RuntimeError`, since GradcheckError inherits from RuntimeError, no changes are necessary. However if you explicitly check for the errors type via `type(error)`, you'll need to update your code to check for `GradcheckError` instead.
Factors out all the logic handling involving `fail_test`, `raise_exception` into 1) a wrapper around gradcheck that uses try/except 2) gradcheck_helper that always raises exception.
This allows us to avoid having to write the `if not x: return False` logic that is scattered throughout gradcheck currently.
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D27920809
Pulled By: soulitzer
fbshipit-source-id: 253aef6d9a3b147ee37a6e37a4ce06437981929a
