Could you, please, point to the most  recent commit in 

https://git.openstack.org/cgit/openstack/nova/   

for which procedure described in

http://wiki.xen.org/wiki/OpenStack_via_DevStack

provide an ability to launch nova instances via  horizion or nova CLI.

I am aware of bug https://bugs.launchpad.net/nova/+bug/1425115

and tried to revert commit http://git.openstack.org/cgit/openstack/nova/commit/?id=0696a5cd5f0fdc08951a074961bb8ce0c3310086
right after stack.sh cloned /opt/stack/nova and was able successfully complete devstack install with nova-compute daemon up and running.
However, finally attempting to launch Cirros instance I've got following errors in /var/log/libvirt/libxl/instance-00000003.log :-

libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /etc/xen/scripts/vif-bridge online [-1] exited with error status 1
libxl: error: libxl_device.c:1085:device_hotplug_child_death_cb: script: ip link set vif1.0 name tap7f39f4aa-d1 failed
libxl: debug: libxl_event.c:618:libxl__ev_xswatch_deregister: watch w=0x7f9e67ee53c0: deregister unregistered
libxl: error: libxl_create.c:1226:domcreate_attach_vtpms: unable to add nic devices

Another approach to test driver described in details in bug

https://bugs.launchpad.net/ubuntu/+source/nova/+bug/1439645

resulted absolutely same errors errors in same log file. 

Thank you.
Boris Derzhavets.