vmrunner: make mac optional, use virtio/tap by default
vmrunner: make mac optional, use virtio/tap by default

AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,alfred-bratterud/IncludeOS,AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,AndreasAakesson/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,ingve/IncludeOS,AnnikaH/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,ingve/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,AnnikaH/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,hioa-cs/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS