Merge r1588367 from branch2: YARN-1947. TestRMDelegationTokens#testRMDTMasterKeyStateOnRollingMasterKey is failing intermittently. (Jian He via junping_du)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1588368 13f79535-47bb-0310-9956-ffa450edef68