YARN-1138. Merging change r1556978 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1556979 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9420. Add percentile or max metric for rpcQueueTime, processing time. Contributed by Liang Xie.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1556984 13f79535-47bb-0310-9956-ffa450edef68
YARN-1579. ActiveRMInfoProto fields should be optional (kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1557002 13f79535-47bb-0310-9956-ffa450edef68