We currently 'defer' in order to acknowledge processed status updates in the scheduler driver.
This is unfortunate because it adds unnecessary delay and unnecessary retries, especially when the scheduler's queue is backed up!
It is sufficient to use 'aborted' to see if we can send a status update. Ideally there would be proper locking on this variable rather than the use of 'volatile', but since we're mostly concerned about the driver aborting on the same thread as the status update was processed, I've left it as is.
This will also be beneficial when we send status updates through the master as is required for
MESOS-1389 and the other reconciliation tickets.