[Resubmission][Gradient Compression] Refactor default_hooks.py and powerSGD_hook.py by creating a util function that make a vanilla allreduce future (#51400)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51400
Resubmission of #51094
Address https://github.com/pytorch/pytorch/pull/50973#discussion_r564229818
Original PR issue: Investigate Applying PowerSGD to Communication Hook for Gradient Compression #47202
ghstack-source-id: 120725690
Test Plan:
buck test mode/dev-nosan caffe2/test/distributed:c10d -- test_powerSGD_ddp_comm_hook_nccl
buck test mode/dev-nosan caffe2/test/distributed:c10d -- test_default_ddp_comm_hooks_nccl
Reviewed By: rohan-varma
Differential Revision: D26162333
fbshipit-source-id: ccc2eae5383a23673e00d61cb5570fb8bf749cd0
