In common_distributed, fix TEST_SKIPS multiprocessing manager (#44525)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44525
Since `TEST_SKIPS` is a global multiprocessing.manager, this was causing
issues when one test would fail and make the rest of the tests fail during
setup due to networking errors.
See the failed CI job: https://app.circleci.com/pipelines/github/pytorch/pytorch/212491/workflows/0450151d-ca09-4cf6-863d-272de6ed917f/jobs/7389065 for an example, where `test_ddp_backward` failed but then caused the rest of the tests to fail at the line `test_skips.update(TEST_SKIPS)`.
To fix this issue, at the end of every test we revert `TEST_SKIPS` back to a regular dict, and redo the conversion to a `mulitiprocessing.Manager` in the next test, which prevents these errors.
ghstack-source-id: 111844724
Test Plan: CI
Reviewed By: malfet
Differential Revision: D23641618
fbshipit-source-id: 27ce823968ece9804bb4dda898ffac43ef732b89
