OAK-2069: Log details of _lastRev recovery

Merged revisions 1622201 and 1622207 from trunk

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1622208 13f79535-47bb-0310-9956-ffa450edef68
OAK-2007 - MongoBlobStore improvements
Merged r1622197 from trunk



git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1622212 13f79535-47bb-0310-9956-ffa450edef68