Modify Pipe to return an RRef. (#47829)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47829
As per proposal in https://github.com/pytorch/pytorch/issues/44827,
the API needs to return an RRef to support inter-host pipelining.
For now, we just return a local RRef and only support pipeline on a single
host. But having this change in the API upfront ensures we don't make any BC
breaking changes later.
ghstack-source-id: 118366784
Test Plan: waitforbuildbot
Reviewed By: rohan-varma
Differential Revision: D24914022
fbshipit-source-id: e711e7d12efa45645f752f0e5e776a3d845f3ef5
