Improve test_proper_exit error printing (#20166)
Summary:
This doesn't have `strace` yet. But still have `faulthandler` to print stack traces at hanging. Also part of an attempt to isolate changes from #19228 .
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20166
Differential Revision: D15536504
Pulled By: ezyang
fbshipit-source-id: fe6e6e2e9899f30d8167436d7bc62b42883a3356
