OAK-753: add tests for hidden tree

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1467264 13f79535-47bb-0310-9956-ffa450edef68
simplify, avoid multiple calls to toString

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1467265 13f79535-47bb-0310-9956-ffa450edef68