Add test to verify dist_autograd doesn't populate .grad field. (#33949)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33949
ghstack-source-id: 99419830
Test Plan: waitforbuildbot
Differential Revision: D20165254
fbshipit-source-id: ef4413637b1568d81e4aca053838230025df6bba
