YARN-1188. The context of QueueMetrics becomes default when using FairScheduler (Akira Ajisaka via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1525517 13f79535-47bb-0310-9956-ffa450edef68
Fix credit for YARN-1188

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1525519 13f79535-47bb-0310-9956-ffa450edef68