Set storage class based on region

For zonal clusters we cannot use regional storage. gitlab-com/gl-infra/delivery#1260 (comment 424210769)

By default, we were using this StorageClass:

  - apiVersion: storage.k8s.io/v1
    kind: StorageClass
    metadata:
      name: standard-regional-east1
    provisioner: kubernetes.io/gce-pd
    parameters:
      type: pd-standard
      replication-type: regional-pd
      zones: us-east1-b, us-east1-c, us-east1-d

For zonal clusters, this sets a newly defined storage class.