HDFS-4512. Cover package org.apache.hadoop.hdfs.server.common with tests. Contributed by Vadim Bondarev.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1528097 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd