Cleanup misreported failed builds

[agjohnson]

A number of cases will cause a build to exist, stuck in a Building or Cloning state. While we should be addressing these problems as they come up, we should also be doing something to eventually set these builds to a Failed state.

Some possible fixes and other notes:

• Scheduled task to search for these builds, mark as failed. Run this hourly perhaps?
• Report builds that have silently failed for tracking
• Address more issues around build failure, try to catch failure states more. This is tougher as reproducing the queue state and everything else that lead to the failure might be impossible.