skip import nccl and gloo_gpu in cpu machine (#22522)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22522
Skip importing nccl and gloo_gpu modules in cpu machine
Reviewed By: bddppq
Differential Revision: D16115827
fbshipit-source-id: 329b7a0bb5eccb78c9e772bdab5db7c79b546d55
