[TensorPipe] Re-enable dist optimizer tests (#39441)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39441
This is the last test suite to be enabled for TensorPipe.
ghstack-source-id: 105166757
Test Plan: Ran the tests, hundreds of times each, in different build modes.
Differential Revision: D21858975
fbshipit-source-id: ee0a7e64b77b4b1974f031207031cc14afb3a8c2
