OAK-619 Lock-free MongoMK implementation
- Restructure tests (use MemoryDocumentStore based MongoMK where possible)
- Remove duplicate code
- Enable more tests

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1467988 13f79535-47bb-0310-9956-ffa450edef68