Enable printing to stderr for test_proper_exit for better debugging (#18458)
Summary:
related to https://github.com/pytorch/pytorch/issues/16608
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18458
Differential Revision: D14611718
Pulled By: soumith
fbshipit-source-id: 6dc903ff2d32b9c3b76470869d1f4e9a67f706df
