Partially implements blueprint nova-api-samples
fixes bug 1130609
The XML serializer for the update method in the os-services API extensions was
not serializing the "updated_at" field because of a typo in the code.
In this change we added api_samples for the XML output.
Change-Id: I9fff0677e9bad650b19e559b3ed6e9bc0ffe8c3c