Handle non-root disks in infrastructure.libvirt.domains

[tacerus]

Allocate qcow2 images for disks other than root. Non existing disks can be created using qemu-img create, which is slightly different than the cp used for root disks. But existing disks can be resized using the same logic as already present for root disks. Hence maybe adjusting the logic to iterate over all disks, and simply conditionalizing the creation for root would be easiest.