Enable dns cache for k8s-infra-prow-build, cleanup gke-cluster module

[spiffxp]

Followup to #1680 which added the dns cache option, and enabled for k8s-infra-prow-build-trusted

I did some cleanup while I was here, see commits for details

[spiffxp]

/cc @chaodaiG
you opened previous pr
/cc @michelle192837
test-infra-oncall

[chaodaiG]

LGTM

/hold
Do we also need to specify minimum terraform version so that the changes from this PR always work?

[k8s-ci-robot]

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[spiffxp]

/hold cancel

Do we also need to specify minimum terraform version so that the changes from this PR always work

We use version constraints in the individual clusters, e.g.

k8s.io/infra/gcp/clusters/projects/k8s-infra-prow-build/prow-build/00-provider.tf

Lines 8 to 20 in e5f748a

	terraform {
	required_version = "~> 0.12.20"
	backend "gcs" {
	bucket = "k8s-infra-clusters-terraform"
	prefix = "k8s-infra-prow-build/prow-build" // $project_name/$cluster_name
	}
	required_providers {
	google = "~> 3.46.0"
	google-beta = "~> 3.46.0"
	}
	}

But, you're right, there are definite gaps:

• we don't specify constraints within our terraform modules, since they're intended to be internal-only I have been lazy about this (ref: https://www.terraform.io/docs/language/modules/develop/providers.html#provider-version-constraints-in-modules) actually we absolutely do, I missed this e.g. https://github.com/kubernetes/k8s.io/blob/main/infra/gcp/clusters/modules/gke-cluster/versions.tf
• we're not doing any kind of presubmit testing of our terraform, I glanced at starting with terraform validate but won't have time today (will try to open an issue)

[spiffxp]

Ran terraform apply, timestamps for updates to the control plane

$ gcloud container operations list --project=k8s-infra-prow-build --filter="startTime>='2021-02-19'" --format="table(startTime,endTime,operationType,name,status)"
START_TIME                      END_TIME                        TYPE            NAME                              STATUS
2021-02-19T17:29:29.862954192Z  2021-02-19T17:29:30.046259487Z  UPDATE_CLUSTER  operation-1613755769862-3158504f  DONE
2021-02-19T17:29:40.181746963Z  2021-02-19T17:57:21.542807273Z  UPDATE_CLUSTER  operation-1613755780181-48a49af1  DONE

Since nodes need to be recreated for this to take effect, I would rather batch this up with upgrading the cluster to v1.17

[spiffxp]

#1541 (comment) - upgrading node pool now, this will take some time to complete, will verify whether addon has deployed afterward