Mesos roles

[opadron]

Adds new roles for provisioning Mesos nodes + some other big commits in this PR. Sorry for the relatively large PR, but adding Mesos turns out to touch a lot of other things.

Breakdown of changes:

• Add fixes/tweaks in other roles in preparation for Mesos. (4 commits)
• Reorganize documentation. (1 commit)
• Reorganize example playbooks. (1 commit)
• Add some useful files for development. (1 commit)
  • Not strictly necessary, but was helpful during development, so I've included it here.
• Add Mesos roles, proper. (1 commit)
• Add a "gobig" example playbook set, showing what all services look like in action together. (1 commit)

[kotfic]

@opadron do you think you could add a note to the readme that describes the group initials you are using?

[cpatrick]

This LGTM. I'm looking forward to a demo.