Automatic merge from submit-queue (batch tested with PRs 37092, 37850)
Turns on dns horizontal scaling tests for GKE
Seems like the dns-autoscaler is already enabled in [this recent gke build](https://k8s-gubernator.appspot.com/build/kubernetes-jenkins/logs/ci-kubernetes-e2e-gci-gke/769/).
Turning on the corresponding e2e tests to increase test coverage.
Probably better to wait for this fix#37261 to go in first.
@bowei @bprashanth
cc @maisem @roberthbailey
The e2e tests cover cases like cluster size changed, parameters
changed, ConfigMap got deleted, autoscaler pod got deleted, etc.
They are separated into a fast part(could be run parallelly) and
a slow part(put in [serial]). The fast part of the e2e tests cost
around 50 seconds to run.
