YARN-2865. Fixed RM to always create a new RMContext when transtions from StandBy to Active. Contributed by Rohith Sharmaks
(cherry picked from commit 9cb8b75ba57f18639492bfa3b7e7c11c00bb3d3b)
YARN-2802. ClusterMetrics to include AM launch and register delays. (Zhihai Xu via kasha)
(cherry picked from commit f9f8e750edbe6db453f0a845e2ed49ede66e0e8a)
YARN-2315. FairScheduler: Set current capacity in addition to capacity. (Zhihai Xu via kasha)
(cherry picked from commit a9a0cc3679432774154a07d3157ffa0a43e0bf01)