Added support for managing multiple repositories

As briefly discussed (with Zach), I've backported the version of puppet-pkgng I use at my employer, which supports managing multiple repositories. I use this in combination with a poudriere setup, which exports pkgng::repo resources to use on my other systems.

The way I chose the parameters for pkgng::repo (for instance to define host instead of whole URL) allows me to use the resource in combination with managing firewalls more easily.