HBASE-8662 [rest] support impersonation

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1503337 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8662 [rest] support impersonation - ADDENDUM

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1503360 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8662 [rest] support impersonation - ADDENDUM 2

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1503387 13f79535-47bb-0310-9956-ffa450edef68
Fix mistake spotted by Benoit

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1503398 13f79535-47bb-0310-9956-ffa450edef68