Adding 2.0.5-alpha release to CHANGES.txt files of branch-2

Also updating current version to 2.1.0-beta in the CHANGES.txt files

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1488585 13f79535-47bb-0310-9956-ffa450edef68
Setting artifact versions to 2.1.0-SNAPSHOT to refrecl recent release of 2,0.5-alpha

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1488586 13f79535-47bb-0310-9956-ffa450edef68