More explicit fail in AutoscaleTest (#7051)
More explicit fail in AutoscaleTest (#7051)

* the problem is that when the error message is returned to the errgroup
it then logs it and marks the test as failing but the test runs futher;
it is then not clear why the test failed unless you have detailed
knowledge of the test
* this PR makes the failures explicit and also helps Prow highlight the
given section of the test because it detects "FAIL" in the string
knative/serving,knative/serving