Consider not overriding babel-runtime's Promise

[UltCombo]

We currently override babel-runtime's Promise in Harmonic's CLI mode so that we can report unhandled promise rejections in Node.js (io.js supports this natively).

We should remove this hack once Node.js and io.js are merged and Node.js 0.10-0.12 are deprecated or obsolete. But until then, we should at least add unit tests to make sure this is working as intended.

Note: The Harmonic API will return promises, so the error handling is up to the consumer in this case.