Qonos worker should delete schedules when receiving a job for an instance that no longer exists

Added new method that uses qonos_client to delete a schedule. Occurs when _create_image can't find an instance, an instance no longer exists, or the instance has scheduling disabled. Modified mox tests to expect these calls.

Fixes rm721
Merge pull request #243 from jaredculp/qonos_worker_b721

Qonos worker should delete schedules when receiving a job for an instanc...