Transform aggregate.add_host notification

The aggregate.add_host.start and aggregate.add_host.end notifications
has been transformed to the versioned notification framework.

Note that the legacy event_type was aggregate.addhost but the versioned
notification is named to aggregate.add_host to keep the naming consistent
with the other event_types.

Implements: bp versioned-notification-transformation-queens
Change-Id: I980d89f47b944116e5fc9cedd74c43bbd88fbeae

doc/notification_samples/aggregate-add_host-start.json

@@ -0,0 +1,19 @@
+{
+    "priority": "INFO",
+    "payload": {
+        "nova_object.version": "1.1",
+        "nova_object.namespace": "nova",
+        "nova_object.name": "AggregatePayload",
+        "nova_object.data": {
+            "name": "my-aggregate",
+            "metadata": {
+                "availability_zone": "nova"
+            },
+            "hosts": [],
+            "id": 1,
+            "uuid": "788608ec-ebdc-45c5-bc7f-e5f24ab92c80"
+        }
+    },
+    "event_type": "aggregate.add_host.start",
+    "publisher_id": "nova-api:fake-mini"
+}