Add support for rhel & centos

I've added support for RedHat Enterprise Linux and CentOS to this role, along with serverspec tests that work with [`test-kitchen`][1] and [kitchen-ansible][2].  (Note:  If you want to test these yourself, you'll have to use my [forked version][3] of kitchen-ansible for now)

[1]: https://github.com/test-kitchen/test-kitchen
[2]: https://github.com/neillturner/kitchen-ansible
[3]: https://github.com/trinitronx/kitchen-ansible