The simplestreams service relies on the Keystone Service catalog.
To help debug any issues occurring during test execution, log the
contents of the Keystone service catalog in the event of failure.
Related-Bug: #1930654
Use action to complete initial image sync for the gss charm.
This avoids races where the images end up in the wrong locations
and allows the tests to actually know when images should be
discoverable.
Update tests to wait for at least four images (20.04 is synced
by default).