add raw_host option

This isn't ready for production, but I wanted to suggest it as a strategy.

In #127 it was mentioned vhost was getting overloaded, but it occurred to me, that nginx should be doing a lot of the checks, and not puppet.

This raw_host could then be used to help simplify the vhost, as well giving people more flexibility.

Feel free to criticise, I've only been looking at puppet for a week.