You are probably missing this step:

virt-sysprep -d {libvirt-domain}

^^ Basically this goes through and deletes /etc/udev/rules.d/70-persistent-net.rules and it cleans up the /etc/network/interfaces. If you can't use it then just delete 70-persistent-net.rules before shutting the VM down and setup eth0 to use DHCP without any static addressing. I believe it does a few other things too like history -c.

Then you can do something similar to the Centos build to allow logs: ( To find the exact info you could get one of the ubuntu provided images, then go through and look at their settings in the cloud.cfg and the same files you modify here. )

In order for nova console-log to work properly on CentOS 6.x, guests you may need to add the following lines to /boot/grub/menu.lst

serial --unit=0 --speed=115200 terminal --timeout=10 console serial

Edit the kernel line to add the console entries

kernel ... console=tty0 console=ttyS0,115200n8

virt-sysprep can customize the image how you want. http://libguestfs.org/virt-builder.1.html (virt-builder) can create the image from scratch with customizations.