vagrant-libvirt support

This commits adds basic support to use the Vagrantfile with vagrant-libvirt 
plugin.
On Mon, Dec 1, 2014 at 6:46 AM, Ivan Necas <notifications@github.com> wrote:
>
> @purpleidea this is the branch used for building the f20 image, right? https://github.com/purpleidea/vagrant-builder/tree/feat/fedora-20

I can actually pull this into git master if you like. I think it
should be in the CentOS-7.0 family now, instead of needing a separate
f20 branch. Patches welcome, or if you bug me enough, I can do it.