opsys.py: Make Ubuntu 22.04 default
opsys.py: Make Ubuntu 22.04 default

Signed-off-by: David Galloway <3e8255e6da72a95698e467f9b9abf7f6d6acde87@redhat.com>

ceph/teuthology,ktdreyer/teuthology,ceph/teuthology,ktdreyer/teuthology