libvirt provider #6

On Linux at-least, libvirt, QEMU and KVM is the most capable, performant and development friendly virtualization. For comparison, Vagrant on Linux seems both messy in general and Oracle VirtualBox centric. Vagrant could be another provider.

A LibVirt provider, as a peer to AmazonEC2 with comparably ability to launch (via Image, COW), provision, terminate would be an excellent development and integration testing tool.

This would also drive a cleanup pass, and possibly lead to a provider base class extracted from AmazonEC2.