Basic auth deprecated on latest GKE (Cloud Foundation templates)

Using the [GKE Cloud Foundation templates](https://github.com/GoogleCloudPlatform/deploymentmanager-samples/tree/master/community/cloud-foundation/templates/gke) to upgrade GKE to version 1.12+ will throw an error like the following:

```
ERROR: (gcloud.deployment-manager.deployments.update) Error in Operation [operation-xxx]: errors:
- code: REFERENCE_VALUE_NOT_FOUND
location: /deployments/xxx/resources/xxx->$.properties
message: |-
The reference 'masterAuth.clientCertificate' is not found, reason:
The resource 'xxx' exists, but the reference value does not.
```

It looks like `masterAuth` has been deprecated as of [June 3rd 2019](https://cloud.google.com/kubernetes-engine/docs/release-notes#june_3_2019):
_"Basic authentication and client certificate issuance are disabled by default for clusters created with GKE 1.12 and higher. We recommend switching your clusters to use OpenID instead."_