Vagrant scripts for dev environment

While I was at EuroPython last week, I put together this Vagrant script to help people set up their Devstack/ZeroCloud environment. It may need some more work and better documentation, but it's a start.

I did this because I found it tedious and error-prone to do everything by hand (see `doc/Hacking.md`).

Note: If you're running Linux in VirtualBox or on a Rackspace cloud server, the default virt backend for Vagrant (VirtualBox) will not work.