Downgrading libvirt and qemu packages to 2.5.0-3ubuntu5.6~cloud1 and 1:2.8+dfsg-3ubuntu2.9~cloud1 fix the issue.
Downgrading libvirt and qemu packages to 2.5.0-3ubuntu5. 6~cloud1 and 1:2.8+dfsg- 3ubuntu2. 9~cloud1 fix the issue.