Clean up Revision test code.

[mattmoor]

Refactor the Revision controller tests to use the pattern adopted in #1216.

[mattmoor]

In order to use the new testing style I believe all Get() operations must be through the Informer's Lister. This means we need to convert the ConfigMap Get for the fluentd ConfigMap. I'd avoided this because the Informer we're passed is filtered to our system namespace.

[mattmoor]

I think the main piece of this that's remaining is coverage of the VPA code, which is blocked on the VPA stuff switching to informers/listers. Especially with #1501 available, the VPA stuff is definitely the most obvious gap in our coverage.

cc @josephburnett

[mattmoor]

Going to close this in favor of move the VPA stuff into the autoscaling controller.