HDFS-4337. Backport HDFS-4240: For nodegroup-aware block placement, when a node is excluded, the nodes in the same nodegroup should also be excluded.  Contributed by Meng Gong


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1427762 13f79535-47bb-0310-9956-ffa450edef68