executor: fix deleting a machine during TRAINING/QUICK_CHECK
When we are trying to remove a machine while it is training, we end up in a deadlock because MaRS holds the db lock, and the DUT thread is trying to update the machine's readiness for service but fails to acquire the MaRS lock.
Break this deadlock by exiting the thread as soon as we are done executing the Sergeant Hartman task, skipping any state update.