minor improvement


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1629876 13f79535-47bb-0310-9956-ffa450edef68
OAK-2158 : Fail for ACEs created for the admin principal

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1629878 13f79535-47bb-0310-9956-ffa450edef68