Adding virt-spawn script

Last couple of months, I was pretty successful with my `fvb` script which I am
renaming and offering here.

To test this, just run it, it will create libvirt domain "nightly.local.lan"
with nightly foreman bats installation. Before doing that, use `--install-deps`
to get required packages.

Use the `--help` option to get more info about dnsmasq integration to get your
hostnames working and other nice stuff.

This only works on Fedora 20+ because of virt-builder.

I will maintain this as I use this everyday. The reason to push it into this
repo is this is tightly (and always will be) tightly integrated to
foreman-bats.