update defaults

Kali VM images have default ram and CPU values, so I added those default values to the vagrantfile template.

For the libvirt configuration, I also switched the video to virtio and graphics to spice, much more modern defaults. I also added the qemu and spice channels to allow host-to-guest communication. These channels enable auto-resizing displays, shutdown signals, and shared clipboard.

Overall these changes should improve user experience using vagrant VMs, especially for the libvirt provider.