Bug 1075475 - [CostControl] Fix unit tests with a newer mocha r=salva r=...

...djf
here there was a race because we were not waiting for `request*SimIcc` results before moving to the next test. So now I'm waiting for each result using Promise.all.

It would be easier to convert request*SimIcc to return promises directly, but since their callback uses the same prototype than the promises callback (`resolve, reject` === `success, error`), it's quite easy to do here :)