looks like bad conflict resolution.
In https://github.com/edx/configuration/blob/jarv/common-refactor/playbooks/roles/mongo/defaults/main.yml mongo_dbpath is set twice. I'll update it so that it is `mongo_dbpath: "{{ mongo_data_dir }}/mongodb"`

I don't think we need the symlink since in mongodb.conf.j2 we have `dbpath={{ mongo_dbpath }}`

mongo_app_dir isn't used anywhere so it can be removed, I was setting the boilerplate directories (app, data) for every role.