Don't use update_attribute(s) in the models.
Test cancelling a Run before it starts running.

If the run is queued but not running yet then it should just be removed from the
queue.
Add Run#pending?

Fix some of the fixtures (and tests) that were wrong relating to this method
being absent until now.
Add Run#initialized?
Add Run#incomplete?

This is not quite !complete? but is a catch-all for pending?, initialized?
and running?
Allow cancelling a run if its delayed_job fails.