Retry sync_step even on UnrecoverableException

Summary:
There are cases which seem to hit in Jenins where the job says its active, yet Jenkins does not yet report
the job as existing.

This will allow us to still mark the step as the correct failed state, but will retry using the normal behavior.

Reviewers: cf

Reviewed By: cf

Differential Revision: https://tails.corp.dropbox.com/D45172