Deduplicate service status notification samples

This patch refactors the sample files of service-create, service-delete
and service-update notifications to use a common ServiceStatusPayload
sample data.

Change-Id: I708ce5423806d2913e77abbe338aec970a5009dc

doc/notification_samples/service-delete.json

@@ -1,22 +1,7 @@
 {
     "priority": "INFO",
     "payload": {
-        "nova_object.namespace": "nova",
-        "nova_object.name": "ServiceStatusPayload",
-        "nova_object.version": "1.1",
-        "nova_object.data": {
-            "host": "host2",
-            "disabled": false,
-            "last_seen_up": null,
-            "binary": "nova-compute",
-            "topic": "compute",
-            "disabled_reason": null,
-            "report_count": 0,
-            "forced_down": false,
-            "version": 23,
-            "availability_zone": null,
-            "uuid": "32887c0a-5063-4d39-826f-4903c241c376"
-        }
+        "$ref": "common_payloads/ServiceStatusPayload.json#"
     },
     "event_type": "service.delete",
     "publisher_id": "nova-compute:host2"