[BE] Fix FSDP flaky test (#71525)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71525
Closes https://github.com/pytorch/pytorch/issues/71496. Use file init
for test as opposed to TCP init which runs into some port racing conditions as
seen in the failures for that issue.
ghstack-source-id: 147300691
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D33676165
fbshipit-source-id: fcf83f7c7541d3521d3e38481195b0c7cb081691
(cherry picked from commit ea091c4af7d864e4d2ebcda6f72d04e17ae7bd82)
