Added rewrite-host-header to system model

Looks good but I have a couple of questions.
* Is there a reason you don't want to continue to use the [Bento boxes](https://github.com/opscode/bento) that Opscode provides?
* It looks like Opscode added the Vagrant provider to the Bento box URLs. If we do use their ubuntu-14.04 box can we update the other URLs to match?
* Can we drop the ubuntu-10.04 box?