Add tags to instance.create Notification

This patch added a new field 'tags' to InstanceCreatePayload.

Partial-implement: bp additional-notification-fields-for-searchlight
Partial-implement: blueprint support-tag-instance-when-boot

Change-Id: Iefaa9da4e136fd5e823bf7b11c8aa5b4cd6d7de8

doc/notification_samples/instance-create-error.json

@@ -49,6 +49,7 @@
             "state":"building",
             "task_state":null,
             "power_state":"pending",
+            "tags":["tag"],
             "tenant_id":"6f70656e737461636b20342065766572",
             "terminated_at":null,
             "auto_disk_config":"MANUAL",
@@ -79,7 +80,7 @@
         },
         "nova_object.name":"InstanceCreatePayload",
         "nova_object.namespace":"nova",
-        "nova_object.version":"1.5"
+        "nova_object.version":"1.6"
     },
     "priority":"ERROR",
     "publisher_id":"nova-compute:compute"