[DDP Communication Hook] Simplify the implementation of parseHookResult of PythonCommHook (#62389)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62389
Simplify the implementation of `parseHookResult` of `PythonCommHook`, by not directly accepting the output of allreduce, which is a tensor list.
Address the comment on https://github.com/pytorch/pytorch/pull/62074#discussion_r675303280
Additionally, formatter is also applied to `OptimizerHookState` and `hook_then_optimizer`.
ghstack-source-id: 134626246
Test Plan:
buck test mode/dev-nosan caffe2/test/distributed:c10d
buck test mode/dev-nosan caffe2/test/distributed:distributed_nccl_fork
Reviewed By: rohan-varma
Differential Revision: D29982485
fbshipit-source-id: 5b27cc5ef09d2f87c1ade4c0feef7eacc1af3a9a
