HDFS-5398. NameNode changes to process storage reports per storage directory.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2832@1534847 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5390. Send one incremental block report per storage directory.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-2832@1534891 13f79535-47bb-0310-9956-ffa450edef68