OAK-1295 - Recovery for missing _lastRev updates

-- Implemented the check for wether recovery is required by any node as Mongo query
-- Added a scheduled job for running the recovery check every 1 min by default

Also changed Clock handling by adding a resetToDefault method which resets the clock back to simple instead of doing that via passing null

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1584287 13f79535-47bb-0310-9956-ffa450edef68