Mesos roles

here are roles for `mesos-master` and `mesos-slave` called `mesos-leader` and `mesos-follower`. They're currently using `redjack/mesos:0.21.0`, but any Mesos image would do the trick, with modifications to linking for the follower.

Reviewers: @stevendborrelli 

This is the first draft of the PR, there are a few things left to be done:

- [ ] remove or re-use the data volume for logs and `work_dir`.
- [ ] revert the changes to the zookeeper role

…plus anything else that review finds.