WIP- Merging back my ansible-mesos fork.

I forked ansible-mesos and https://github.com/mhamrah/ansible-marathon some time ago, and I wanted to get these branches back in sync so we can team up on this role. This PR is to give you an FYI and receive feedback for the merge. I noticed @kienpham2000 was making similar changes, and figured why duplicate. 

Major changes:

* Version 0.20.1 of mesos
* Containerizer is docker,mesos by default
* Provide a deconstructed zookeeper/mesos master url so a playbook can easily create a master cluster based on ```groupvars```
* RedHat family support (issues with zookeeper installation)
* Sourced environment variables for settings, as per Mesos documentation.

Let me know what you think.
Totally agree. I think this was there from the fork, or an old version that got out of sync.

BTW, do you guys have a way of running automated tests on this locally? I believe @JasonGiedymin mentioned something over the summer. Would be nice to test provisioning with vagrant (I was kind of doing it with packer/docker but wasn't as fluid as I wanted).