move HADOOP-10781 to 2.6

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1608936 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6627. Rename DataNode#checkWriteAccess to checkReadAccess. Contributed by Liang Xie.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1608940 13f79535-47bb-0310-9956-ffa450edef68