Add examples/tests that work against an on-cluster registry

[mattmoor]

To test true isolation from Google, it should be possible to run a build publishing to an on-cluster registry (most testing currently works against GCR), so that subsequent deployments may pull the image from there.

In the simplest case, testing this in an unauthenticated (e.g. cluster-visible) setup is probably a good starting point. Beyond that we get into non-GCR authentication questions, which is a separate issue.

[mattmoor]

Perhaps useful: https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/registry#private-docker-registry-in-kubernetes

[knative-housekeeping-robot]

Issues go stale after 90d of inactivity. Mark the issue as fresh with /remove-lifecycle stale. Stale issues rot after an additional 30d of inactivity and eventually close. If this issue is safe to close now please do so with /close. Send feedback to sig-testing, kubernetes/test-infra and/or fejta. /lifecycle stale