Revert D29794666: Remove faulty process group code
Test Plan: revert-hammer
Differential Revision:
D29794666 (https://github.com/pytorch/pytorch/commit/afe3644321366c3e7c365ed2d8ed0454abe8438e)
Original commit changeset: 0b35191cc072
fbshipit-source-id: 6467bc5100f4115f2fdb385e205740cd68c89743
