Don't use Ubuntu minimal in the Rocky and Queens scenario jobs

It seems that tests like test_subport_connectivity and
test_connectivity_min_max_mtu aren't running fine with Ubuntu minimal
image used as guest OS on the old branches stable/Rocky and
stable/Queens.
As both of those branches are now in the EM phase, let's simply use
regular Ubuntu cloud image in those jobs.

Closes-Bug: #1950795
Change-Id: I3c4297a5df1b30c83050a47a3c08b6623bb00abb
2 files changed