Add option to allow resolving non-200 responses

[diosmosis]

Currently, using usePromise: true will result in non-200 responses being rejected. When writing failure tests w/ a generator flow control library (like co), this can result in strange looking code, for example:

var client = // ... create Swagger client w/ usePromise: true

it('should respond w/ 404', function * () {
    var response;
    try {
        yield client.widgets.getWidget({ widgetId: 'unknown-id' });
    } catch (r) {
        response = r;
    }

    expect(response.status).to.equal(404);
});

It would be great if there was something like request-promise's simple: false option that lets us get non-200 responses like so:

it('should respond w/ 404', function * () {
    var response = yield client.widgets.getWidget({ widgetId: 'unknown-id' });
    expect(response.status).to.equal(404);
});

[fehguy]

OK, I can see where that would be convenient but certainly not the default (like what you did suggest). The behavior is to treat the error responses like errors and require you to catch them. I have added a couple tests to ensure this keeps working by default.

If you'd like to send a PR, we can set that option to allow all responses to flow through the success resolve, and it can be handled like you're proposing.

I'll close this out when the tests are committed, and you can add a PR to give this option, assuming you have time.