Return the body alongside the status in the `baseRetryPolicy` in case of error

Presently, when the following case is true inside the `baseRetryPolicy`:

```
if resp.StatusCode == 0 || (resp.StatusCode >= 500 && resp.StatusCode != http.StatusNotImplemented) {
```

the only things returned are the `status` and the `statusCode`, however, in some cases, the server returns more information regarding the error within the response's body.

Adding the `response body` to the error returned by the `baseRetryPolicy` would be helpful for logging and debugging purposes.