HBASE-8569. Improve coverage in package org.apache.hadoop.hbase.security. Contributed by Vadim Bondarev and  Andrey Klochkov

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1537986 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd