OAK-1893 - MBean to dump Lucene Index content and related stats

Somehow the mbean classes missed from previous merge. May be due to result of a failed commit. Adding them now

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1621125 13f79535-47bb-0310-9956-ffa450edef68