[travis] Ensure that fetching pull-requests stops when no longer needed.
[worker] Update Travis build statuses every 10 minutes.
[job] Log number of jobs in queue waiting for a Travis notification.
[job] Add a log message whenever the Travis build status is updated.
Fix require.
[log] Make sure errors fit in the log messages table.
[job] Log when a travis build status is received and bumps the attempt count.
[worker] Since jobs get their attempts bumped, the last updated_at status is set again and jobs won't be picked up until in exactly 10 seconds.
[worker] Simply sleep 1 sec after each iteration.
[job] Bump attempt when a job is not included in the build results.
[job] Change travis notification timeout to 6 minutes.

With a retry count of 10 this means a total job will not
take longer than 60 minutes.
[travis] Raise in case of HTTP error status codes.
[job] Cleanup logging.
[job] Perfor query within silence block.
[travis] cleanup
[job] Wrap updating of Travis build statuses in transaction.
[job] Log when a job transitions to having failed.
[job] Change Travis build URL to build ID.
[job] Store build ID instead of build url in the DB.
[job] If the travis build ID is known, no need to check all the builds.