HDFS-1804. Add a new block-volume device choosing policy that looks at free space. Contributed by Aaron T. Myers.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1465184 13f79535-47bb-0310-9956-ffa450edef68
Merge -c 1465188 from trunk to branch-2 to fix MAPREDUCE-5129. Allow tags to JobHistory for deeper analytics. Contributed by Billie Rinaldi.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1465189 13f79535-47bb-0310-9956-ffa450edef68