How do I connect to my libvirt/qemu/guests ? (with no ip address)
vnc is not limited to presenting a GUI; it can also present a graphical view of a shell prompt, just as you'd expect to see on the text console of a standalone box (eg, ALT-F2).
For example, here's me pointing a vnc viewer at the VNC port of one of my locally-hosted QEMU images:
It is, as you see, a non-GUI console, but I could happily log in here nonetheless, even if it had no IP address (as in fact it doesn't). Point your VNC viewer at port 5909 (add 5900 to the argument of -vnc 127.0.0.1:) and you should be fine.