VMs: add virtio video device to vm-template

Debian VMs are not booting without a video device. This is a bug with
our configuration, which we should fix. For now, we are working around
by adding a virtio video interface.

roles/virtual-machines/templates/vm-template.xml

@@ -81,6 +81,12 @@
     </channel>
     <input type='mouse' bus='ps2'/>
     <input type='keyboard' bus='ps2'/>
+    <video>
+      <model type="virtio" heads="1" primary="yes">
+        <acceleration accel3d="no"/>
+      </model>
+      <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0"/>
+    </video>
     <memballoon model='virtio'>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
     </memballoon>