cloud-image-uploader: use stringData instead of data

I mis-read the docs and data needs to be base64 encoded, stringData will
handle it for you.

roles/openshift-apps/cloud-image-uploader/templates/secret.yml

@@ -4,7 +4,7 @@ metadata:
   name: "azure-credentials"
   labels:
     app: "cloud-image-uploader"
-data:
+stringData:
 {% if env == 'staging' %}
   secret: "{{stg_azure_secret}}"
   client_id: "{{stg_azure_client_id}}"