svn merge -c 1416691 from trunk for HDFS-4240. For nodegroup-aware block placement, when a node is excluded, he nodes in the same nodegroup should also be excluded.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1488851 13f79535-47bb-0310-9956-ffa450edef68