More option for storage,network,cpu

[dreadkopp]

I find myself adjusting the guests xml all the time, since i prefer raw images over qcow2, virtio NIC over e1000 and like to set the cpu to the host model.

It would be great to have those options when creating a template / guest:

1. choose storage format
2. choose network interface (we can change its MAC address, why not the type?)
3. choose cpu type