Update JDiff, releasenotes, and CHANGES.txt in branch-1 upon release of 1.2.1.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1510333 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9730. Fix hadoop.spec to add task-log4j.properties. Contributed by Giridharan Kesavan.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1510336 13f79535-47bb-0310-9956-ffa450edef68