Allow RPC to be initialized again after shutdown. (#42723)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42723
This PR is addressing https://github.com/pytorch/pytorch/issues/39340
and allows users to initialize RPC again after shutdown. Major changes in the
PR include:
1. Change to DistAutogradContainer to support this.
2. Ensure PythonRpcHandler is reinitialized appropriately.
3. Use PrefixStore in RPC initialization to ensure each new `init_rpc` uses a
different prefix.
ghstack-source-id: 109805368
Test Plan: waitforbuildbot
Reviewed By: rohan-varma
Differential Revision: D22993909
fbshipit-source-id: 9f1c1e0a58b58b97125f41090601e967f96f70c6
