Added status code and payload to response server log

This is to expose additional information via `request._log`.  This first exposes an object instead of the `err` value, and has two additional properties added to it: `statusCode` and `data`, which represents the raw payload.

In what use case is `err` getting populated?  I can't track down how and with what this value is filled.  I'm wondering if `source._data` could replace the need for `err`.

cc @hueniverse