Nova returns request ids in responses

Nova creates request-ids when a request arrives, and passes it through the system with the context variable. We propose to add this request id to all responses. Additionally, we propose to add support to logging to report this request-id appropriately. Combined, these changes will enable easier troubleshooting, since a user could report a request-id associated with a problematic response and an administrator could more easily find actions associated with that request in system logs.