message: Make service principal optional
  The resource provider will now create a service principal on behalf of the
  user to simplify the create process. Users can still provide a service
  principal if desired.
diff: "type": "object",
  "description": "Kubernetes cluster specific properties",
  "x-ms-discriminator-value": "Kubernetes",
  - "required": [
  - "servicePrincipal"
  - ],
  "properties": {
  "servicePrincipal": {
  "description": "The Azure Service Principal used by Kubernetes",
  