I have followed this bug report only to wind up in a similar predicament. The Error: 'NoneType' object has no attribute 'rfind' was fixed by installing xen-qemu-dm-4.0. However the same configuration issue (trying to boot the guest from a CD) with the 'boot' option exists for me too.
Your configuration looks good unless I've missed something.
Shall we file a new bug for the boot option behavior in the domU configuration
file?
