switch gloo tests back to cpu (#1665)

Summary:
Pull Request resolved: #1665

Also minor refactoring.

Reviewed By: sarckk

Differential Revision: D53149479

fbshipit-source-id: 5c0cb8925118e6a2ad76a7f45c102a2c4a6f518e

Author: henrylhtsang

torchrec/distributed/tests/test_model_parallel_gloo.py

@@ -16,9 +16,9 @@ class ModelParallelTestGloo(ModelParallelBase):
     pass
 
 
-class ModelParallelStateDictTestNccl(ModelParallelStateDictBase):
+class ModelParallelStateDictTestGloo(ModelParallelStateDictBase):
     pass
 
 
-class ModelParallelSparseOnlyTestNccl(ModelParallelSparseOnlyBase):
+class ModelParallelSparseOnlyTestGloo(ModelParallelSparseOnlyBase):
     pass