OAK-519: Migration of custom jr2.x privileges into OAK

Add Angela's PrivilegeMigrator to oak-upgrade.
Not integrated into the main RepositoryUpgrade class yet.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1558101 13f79535-47bb-0310-9956-ffa450edef68