Merge HADOOP-9114. After defined the dfs.checksum.type as the NULL, write file and hflush will through java.lang.ArrayIndexOutOfBoundsException. Contributed by Sathish.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1544190 13f79535-47bb-0310-9956-ffa450edef68