Add support for vagrant openstack provider.

Yo dawg I heard you like abstractions so I put an abstraction in your abstraction.

So this basically lets you use `vagrant up --provider=openstack` to spin up your vagrant vms in an openstack cloud rather than local virtualbox.  there's a few assumptions in there about network names and security groups, but these can be easily modified.    
it should never have been in there in the first place, I had it in there in a previous PR to work around a problem that didn't actually exist.