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

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1536930 13f79535-47bb-0310-9956-ffa450edef68
CHANGES.txt, pom.xml for 0.94.13

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1536938 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/0.94' into 0.94-gd
Merge remote branch 'origin/0.94-gd' into fb-HBASE-8553-0.94-gd