HBASE-9221: Provide interface for getting a User in the client

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1536937 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9221: Provide interface for getting a User in the client: ADDENDUM

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1536944 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd