Comment 14 for bug 1673467

Snipping the interesting parts:

    <type arch='aarch64' machine='virt'>hvm</type>
[...]
  <features>
    <gic version='3'/>
[...]
  <cpu mode='host-model'>
    <model fallback='allow'/>
[...]

That means on Xenial-Newton that worked for you.
Yet as outlined before "worked" is a bit special here as it meant more "passed but didn't work" as outlined in comment #5 - I don't know the details of this.

With that in mind for now lets simplify the Test and try to get Openstack out of the equation for now (although it might eventually be the best place for a solution).

Will update after some tests ...