Comment 2 for bug 1948804

I think this appeared with the switch to Ubuntu minimal:
https://opendev.org/openstack/neutron-tempest-plugin/commit/7e5923ac25769073e34a5500504bb8851978cb0e

guestmount does not seem to be installed by default for bionic
With pinned versions all around, I guess the fix is to switch back to 18.04 server image for train and stein (and older?)