Merge change r1558255 (HDFS-5704) and r1558675 (HDFS-5777) to branch-2: Change OP_UPDATE_BLOCKS with a new OP_ADD_BLOCK,and update the LayoutVersion

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1559224 13f79535-47bb-0310-9956-ffa450edef68