Build NGINX from source with nginx.ng state with support for passing
compile time flags necessary for installing modules such as more headers
by the openresty project.

* added comment for pillar example
 * removed override releasever variable use for CentOS

Needed to add repo management because opensuse doesn't have nginx
in default repo

This reverts commit f6ba9ddb59.

the nginx.ng formula is only compatible with the upcoming feature
release, as noted here:

https://github.com/saltstack-formulas/nginx-formula#nginxng

This argument is only currently available in develop, and thus does not
belong in this formula at this time.