Job save callback should be called without arguments

[schinkowitch]

If I call

jobs.createJob({...}).save(function (error) {
if (error) {
// Unable to save job
} else {
// Job saved!
}
});

The error in the callback is set to the job. It should be undefined.

Ideally, we should be able to test both cases (job saved successfully / job save failed), but that's a new feature.