Clean up the code in the service test (#10756)
Clean up the code in the service test (#10756)

- fix the public items to be private (tests don't export stuff)
- rename the things to follow our standard functional naming.
- remove the comment by Matt, which is 2.5 years old (even before my
  time on the project :-) ).
- make the route ready condition _stronger_ by observing generation too.

Change-Id: Ie43e4ad573b1f0969604967210dedee4361c7855
knative/serving,knative/serving