Clarify error message for Nova notification settings

Previously, the error messages provided no information as to what the
settings should be, they just reported the current value with no
indication of any change that needed to be made. This patch makes them
clearer.

Change-Id: I654df90091e12b9b85ad704312e4ae6c2740ad70

roles/nova_event_callback/tasks/main.yml

@@ -65,7 +65,7 @@
 
 - name: Check Notify Nova settings values
   fail:
-    msg: "Value of {{ item.item }} is set to {{ item.value|bool }}."
+    msg: "{{ item.item }} should be set ro True. Current value: {{ item.value }}."
   when: not item.value|bool or item.value == None
   with_items: "{{ neutron_notify_nova_result.results }}"