OAK-962: RootFuzzIT fails on MongoMK with seed -1091889749
- Use base revision of commit in MongoMK.markAsDeleted()
- Enable test in RootTest and RepositoryTest (RootFuzzIT still fails)

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1515408 13f79535-47bb-0310-9956-ffa450edef68