When adopting oslo.versionedobject, we found that obj_name has been used as a function for VersionedObject class. Unfortunately, in senlin database, we have 'obj_name' column (property) for events. This is making the event objects very difficult to be serialized/deserialized. This patch renames the 'obj_id', 'obj_name', 'obj_type' fields to 'oid', 'oname', and 'otype' respectively. Change-Id: Idcdd979946b0e5289c4b42d2a322324d011954e0