Add support for using VMs instead of containers

[christopherobin]

While we may want to keep ansible in a container (so that we can properly version it), running the tests in containers is currently causing some issues for systemd guests, a solution would be to support multiple "drivers" for starting test VMs.

Supported targets initially would be:

• docker
• qemu/kvm (Linux only)
• xhyve (OSX only)
• virtualbox

To be added later:

• vmware
• xen
• aws
• digitalocean