fix(agent): Align handling of Job unschedule/destroy events

The EventJobDestroyed and EventJobUnscheduled events can be handled
by common code since they both want to accomplish the same thing.
Note that this fixes a bug in HandleEventJobDestroyed where conflicting
Jobs are never bid upon after destruction.
Merge pull request #460 from bcwaldon/local-unload

fix(agent): Only react to EventJobDestroyed if job scheduled locally