Fix lost reference to hash (data) passed into RESTAdapter#ajax

- function passed into new RSVP expects hash reference for ajax data
- reference to hash arg is lost after promise constructor call
- added a local reference in the closure scope to prevent lossing scope
- unit tests mock response with resolved promise so doesn't catch this case

See:
https://github.com/emberjs/data/blob/master/packages/ember-data/lib/adapters/rest_adapter.js#L501-L517
https://github.com/emberjs/data/blob/master/packages/ember-data/tests/integration/adapter/rest_adapter_test.js#L156-L169
https://github.com/emberjs/data/blob/master/packages/ember-data/tests/integration/adapter/rest_adapter_test.js#L34-L42


I noticed the issue using Ember.data canary on 10/8 both the RESTAdapter methods `createRecord` and `updateRecord `did pass my model's data for sending to the server however in the RESTAdapter#ajax the `hash` reference was lost as the promise was created the `hash` was undefined when passed into `adapter.ajaxOptions`. My server responded with `{"meta":{"error":"No Attributes"}}` I looked into the test "integration/adapter/rest_adapter - REST Adapter: create - a payload with a new ID and data applies the updates" and noticed that the `ajaxResponse` function mocks the RESTAdapter#ajax by returning a resolved promise and assigned the ajax options to a variable to compare. Those options are not passed into a RSVP#Promise constructor so the test is not failing. However in an application with a live server the POST and PUT requests are not sending any data.