Like this:
modprobe nbd
cd /var/lib/nova/instances/bed8d7bc-cde2-4bdf-9a6b-ccbd9df70912
qemu-nbd -c /dev/nbd0 disk
partprobe /dev/nbd0
mount /dev/nbd0p2 /mnt
cd /mnt/etc/init.d/
mv rc.platform.manual rc.platform
cd /var/lib/nova/instances/bed8d7bc-cde2-4bdf-9a6b-ccbd9df70912
umount /mnt
qemu-nbd -d /dev/nbd0
virsh start instance-00000325
<serial type=’pty’>
<target port=’0’/>
</serial>
<console type=’pty’>
<target type=’serial’ port=’0’/>
</console>