Fix ASB user and password defaults

roles/ansible_service_broker/vars/openshift-enterprise.yml

@@ -2,8 +2,8 @@
 __ansible_service_broker_registry_type: rhcc
 __ansible_service_broker_registry_name: rh
 __ansible_service_broker_registry_url: "https://registry.redhat.io"
-__ansible_service_broker_registry_user: "{{ oreg_auth_user | default(null) }}"
-__ansible_service_broker_registry_password: "{{ oreg_auth_password | default(null) }}"
+__ansible_service_broker_registry_user: "{{ oreg_auth_user | default(None) }}"
+__ansible_service_broker_registry_password: "{{ oreg_auth_password | default(None) }}"
 __ansible_service_broker_registry_organization: null
 __ansible_service_broker_registry_tag: "{{ openshift_image_tag }}"
 __ansible_service_broker_registry_whitelist: