Make TensorPipe the default backend for RPC (#43246)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43246
Test Plan: Imported from OSS
Reviewed By: osalpekar
Differential Revision: D23206042
Pulled By: osalpekar
fbshipit-source-id: 258481ea9e753cd36c2787183827ca3b81d678e3
