Preparing for hadoop-2.2.0 release.

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HDFS-4817. Moving changelog to Release 2.2.0 section to reflect the backport.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1529751 13f79535-47bb-0310-9956-ffa450edef68
Release notes for hadoop-2.2.0.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1529756 13f79535-47bb-0310-9956-ffa450edef68