When using remote partitioning, each slave worker persists it's current
status in the same job repsository that the master uses. Because of
this, there is no hard need for the master to wait for each worker to
send a formal response once it's work is complete. Instead, the master
(at the cost of polling a db periodically) can determine if the workers
are done by looking up each partition's status in the job repository.
This commit removes the requirement for a reply channel and implements
the polling of the job repository to determine if the workers are done.
BATCH-2332
066c59a390