pytorch

130127ca - Rename `BACKEND` to be `RPC_BACKEND` to be seperated from `COMMUNICATION_BACKEND` like gloo,nccl, in `rpc_test.py` (#27792)

Rename `BACKEND` to be `RPC_BACKEND` to be seperated from `COMMUNICATION_BACKEND` like gloo,nccl, in `rpc_test.py` (#27792) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/27792 Close https://github.com/pytorch/pytorch/issues/27232 ghstack-source-id: 91807741 Differential Revision: D5474297 fbshipit-source-id: 5b230a6857813ec981e5056880abb5859655daa2