Summary:
As expected, this didn't work on the first try. Issues I've fixed:
- Actually switch back to snapshots.
- Use more widely compatible bash location.
- Don't exit (because of `set -e`) if `grep` returns with status 1.
Reviewed By: jknoxville
Differential Revision: D9556770
fbshipit-source-id: 0900e6498e7fc8e16c941e77927005573ca310d5