Fix flaky test_barrier_timeout_global. (#57523)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57523
`_test_barrier_timeout` would run a barrier on rank 1 and sleep for
`timeout` on other ranks. In some cases if the other ranks would be faster,
they would enter the sleep call much earlier than rank 0 would enter barrier.
As a result, they would exit before the timeout is up and rank 0 would receive
a connection closed error instead of a timeout error. This would result in the
barrier call exiting before the timeout and the subsequent assertion failing.
#Closes: https://github.com/pytorch/pytorch/issues/57176
ghstack-source-id: 128278775
Test Plan:
1) waitforbuildbot
2) Tested synthetically by forcing a rank to exit earlier.
Reviewed By: rohan-varma
Differential Revision: D28170821
fbshipit-source-id: a67456a1784dd0657f264c4f5498638e0aa00de2
