Add the port "configured" to the headless Varnish admin Service,
which responds with status 200 when an Ingress is configured, 503
otherwise. This replaces the previous purpose of the Ready state,
to determine if the Pods are currently implementing an Ingress.

This is actually a small change to the Varnish images and the admin
Service, but a wide-ranging change for testing, since we now check
the configured port before verifying a configuration (rather than
wait for the Ready state). Common test code is now in the bash
library test/utils.sh.

This commit also includes a fix for the repeated test of the
ExternalName example, which verifies that the changed IP addresses
for ExternalName Services are picked up by VMOD dynamic. The test
waits for the Ready state of the IngressBackends. The second time
around, kubectl wait sometimes picked up previous versions of the
Pods that were in the process of terminating. These of course never
became Ready, and the wait timed out. Now we wait for those Pods
to delete before proceeding with the second test.