Adding 2.0.6-alpha release to the CHANGES.txt

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1558215 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5677. Need error checking for HA cluster configuration. Contributed by Vincent Sheffer.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1558217 13f79535-47bb-0310-9956-ffa450edef68
YARN-1567. In Fair Scheduler, allow empty queues to change between leaf and parent on allocation file reload (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1558228 13f79535-47bb-0310-9956-ffa450edef68
YARN-1598. HA-related rmadmin commands don't work on a secure cluster (kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1558251 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5704. Change OP_UPDATE_BLOCKS with a new OP_ADD_BLOCK. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1558255 13f79535-47bb-0310-9956-ffa450edef68