Add master to OSS RPC test (#27776)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27776
I think it’s not worth it to equip other `RPCAgent` with collective communication capability, i.e. 1) have GLOO contained in `RPCAgent`, or 2) Implemented ::barrier() and ::drain() based on RPC messaging.
The only use case that does not have a master is the OSS unit test suite, caffe2/test/rpc_test.py.
I think having those unit tests to have a master is simpler than equipping `RPCAgent` with collective communication capability.
Differential Revision: D5445858
fbshipit-source-id: 56ee24703abd8c5b366829430bef657e0f1dfeba
