If this is a Xen Dom0 host with pygrub you can start the vm with:
cd ../../tmp
xl create -c "coreos_production_xen_pygrub.cfg"

Or with pvgrub instead:
xl create -c "coreos_production_xen_pvgrub.cfg"

Detach from the console with ^] and reattach with:
xl console coreos_production_xen-2079-6-0

Kill the vm with:
xl destroy coreos_production_xen-2079-6-0