Turn off host-passthrough in scenario jobs

This was enabled with switch to cirros 0.6.2[1],
but still seeing same tracebacks for cirros vm boot,
this mode is not required for the jobs so let's
turn it off. This may help in the other failures
seen in the Related Bug.

[1] https://review.opendev.org/c/openstack/neutron-tempest-plugin/+/890177
Related-Bug: #2036603

Change-Id: Ifb3972e74434b29a1c6acb9bc131678ba83d66a3
1 file changed