use `settings_travis.js` when running tests locally (bug 1047109)

https://bugzilla.mozilla.org/show_bug.cgi?id=1047109
I like the idea of having a data attr containing a settings object that can override the settings file. We've done that in webpay for a while and we do it in Spartacus too. It works quite nicely and means you can put more service settings in one place.