OAK-633: SegmentMK: Hierarchy of journals

Add hierarchy support also for Mongo journals

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1455635 13f79535-47bb-0310-9956-ffa450edef68
OAK-593: Segment-based MK

Make the security tests pass also with SegmentMK

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1455636 13f79535-47bb-0310-9956-ffa450edef68