Adding Centos Support

I'm happy I came across this repo- I recently had to add Consul support for Centos, and found this the best starting point. I'm new to Ansible, and had to make some semi-opinionated choices to get it working, but I wanted to put it out there in case you were interested.

* Add support for Centos
* Removed NGINX requirement for UI. The ```franklinkim.nginx``` doesn't exist on ansible-galaxy (I couldn't install as a req) nor did I need/want NGINX. Instead, the UI option just enables the UI, and I modified the NGINX support to do a config only, assuming NGINX is already installed. 
* Made Consulate optional (I didn't need this, and seemed to have some install issues)
* Added 127.0.0.1 to /etc/resolve.conf; otherwise, I couldn't get dnsmasq working out-of-box with consul.

Feedback appreciate, or feel free to disregard if you're not interested.

Mike
We still need a nameserver of 127.0.0.1 for consul dns to work locally, but after some research this is in the wrong place. I need to put this in a /etc/resolvconf/resolv.conf.d/consul file. I'll push this change tomorrow.