[RPC] Ensure _wait_all_workers doesn't swallow exception. (#61094)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61094
`_wait_all_workers` was swallowing exceptions and as a result if there
were any errors it would still continue with rpc_agent.join() which would hang
since something already failed before.
To fix this, I've ensured that wait_all_workers throws and in that case we just
proceed with an ungraceful shutdown without joining.
ghstack-source-id: 133160706
Test Plan:
1) Added unit test.
2) waitforbuildbot
Reviewed By: rohan-varma
Differential Revision: D29509286
fbshipit-source-id: 7c3f1c68d712ae2f63e10e0216580db8e9bcc29d
