Cancelling the MR side of the patch .... doesn't really make sense to cancel JobHistory tokens when the job completes, since that's exactly when they're required.
Couple of options for the short term.
1) we could have the RM renew tokens but not cancel them. This still has MR classpath dependency.
2) have the history server issue tokens for a longer period, same as the max-age.
The second option seems better.