Add status propagation tests for Service (#1798)
Add status propagation tests for Service (#1798)

* Add status propagation tests for Service

Fixes #1542

This tests:
1. Route + Config Ready -> Service Ready
2. Config Fails + Route Ready -> Service Fails
3. Config Ready + Route Fails -> Service Fails

These are similar to the propagation tests in
apis/serving/v1alpha1/service_types_test.go but from the reconciler's
perspective.

* Address nit: Fix TODOs

knative/serving,knative/serving