update images used in tests

[minrk]

they were very out of date

for whatever reason, I couldn't run the tests locally with the old images, but they run fine with these

closes #833

[consideRatio]

Nice, closes #833 i think!

I think it could make sense to use latest or similar instead of a version tag here, as we otherwise will fail to update this is require adding a machinery that updates it. Self merge as is or update then merge!

[minrk]

@consideRatio good point! We don't have upper bound on the hub and :latest is the default tag in KubeSpawner.image, so latest is probably the most consistent choice with versions coming from elsewhere.