Automatic merge from submit-queue (batch tested with PRs 49043, 49001, 49057, 49066, 48102)
cluster/gke: If NODE_INSTANCE_GROUP is set, don't execute any bash
Transitional part of kubernetes/test-infra#3307, should be eliminated by kubernetes/test-infra#3330:
Allow NODE_INSTANCE_GROUP to be set externally from `hack/ginkgo-e2e.sh`, which eliminates any cluster/gke use if KUBERNETES_CONFORMANCE_PROVIDER is set to `gke`.
```release-note
NONE
```