Should use backup instead of backup.id in import_record

[Lisa Li]

Please refer to bug 1467841 .
But one place has been left.
                self.backup_rpcapi.import_record(context,
                                                 first_host,
                                                 backup.id, >> here should be backup
                                                 backup_service,
                                                 backup_url,
                                                 backup_hosts)

[Lisa Li (lisali)]

Changes: https://review.openstack.org/197442