* This adds a new 'claimTTL' setting which recycles jobs into the queue
if they have been claimed for longer than that duration (in seconds).
* This also purges jobs for such cases when job retries are not enabled.
* This adds a new job_attempts column and adds an index to improve the
query and semantics for FIFO ordered queues.
Change-Id: Idb6217a694d86a4d6fc881768deed424628f015d
