workaround to set increment-allocations for fair-scheduler

This is to see if we can code a workaround for https://issues.cask.co/browse/CDAP-2877

Essentially:
if FairScheduler is being used, and if minimum-allocation specified is less than the default minimum-increment (1024mb), then override minimum-increment as well.

it would probably require setting a default minimum-increment attribute, which we should be sure matches all distros.