[WIP] STI foreman provider

This creates the models to be used for creating the foreman configuration provider.



This feels like it needs a lot more.
Did I miss anything?
/cc @gmcculloug @brandondunne 
@kbrock So, build the URI with URI::Generic.build + uri.hostname = host and then do uri.to_s when passing it to Rest::Client.  Or, see my Rest::Client PR 333 above, I believe you should be able to pass a URI to it.   It's not yet released but that's the way to do it.