HDFS-6717. Merging change r1614129 from branch-2

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.5@1614132 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10821. Prepare the release notes for Hadoop 2.5.0. (Andrew Wang and Karthik Kambatla via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.5@1614233 13f79535-47bb-0310-9956-ffa450edef68