Comment 4 for bug 1420142

This is fixed in "uvtool (0~bzr99-0ubuntu1) vivid"
Now you might run into this still if you run Trusty (not having this fix as it doesn't need it for its version of libvirt) but then pull in Ubuntnu Cloud Archive Mitaka (or other newer libvirts.

In that case you will get this issue again.
Since UCA is to support an Openstack setup and not for general use the updated uvtool (universe) is not in there.

Workaround: you can easily get the latest from https://launchpad.net/~uvtool-dev/+archive/ubuntu/master and things work again.