Avoid needing config to be in sync between MW and the jobrunner

* This unifies the retry and no-retry code paths so that its easier to use
  the separate job runner service.
* All jobs will use the ack procedure. If no retries are enabled they will
  just get deleted. As a side-effect, abandoned jobs can be seen for a few
  days in the no-retry case, which used to not happen. This could actually
  be useful to know about anyway.

Change-Id: I185092e3696fb336b9edcf19280dcd9a561161d9