fail arc diff if second lfs push errors
We are having issues where people run out of file descriptors and the first git push will succeed, but the
second one will not. We'd like the diff to not be created in this case as it leads to weird behavior like our tests
running against 0 changed files.
Test Plan: none
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Differential Revision: https://secure.phabricator.com/D21471