HDFS-5747. Fix NPEs in BlockManager. (Arpit Agarwal)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1557289 13f79535-47bb-0310-9956-ffa450edef68
YARN-1166. Fixed app-specific and attempt-specific QueueMetrics to be triggered by accordingly app event and attempt event. Contributed by Zhijie Shen

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1557296 13f79535-47bb-0310-9956-ffa450edef68