YARN-4752. Improved preemption in FairScheduler. (kasha)

YARN-5605. Preempt containers (all on one node) to meet the requirement of starved applications
YARN-5821. Drop left-over preemption-related code and clean up method visibilities in the Schedulable hierarchy
YARN-5783. Verify identification of starved applications.
YARN-5819. Verify fairshare and minshare preemption
YARN-5885. Cleanup YARN-4752 branch for merge

Change-Id: Iee0962377d019dd64dc69a020725d2eaf360858c
22 files changed