Follow-up of #860 and #791 to fix:
File "./zaza/openstack/charm_tests/test_utils.py", line 798, in launch_guest
return configure_guest.launch_instance(
File "./zaza/openstack/configure/guest.py", line 128, in launch_instance
image_name = image_name or boot_tests[instance_key]['image_name']
KeyError: 'jammy'