Bug 1049916 - Create Firefox Accounts smoke tests to validate user authe...

...ntication R=spenrose
yep.  I shamelessly copied it from browser: 
https://github.com/mozilla-b2g/gaia/blob/master/apps/browser/test/marionette/lib/server.js
Perhaps move both to: 
https://github.com/mozilla-b2g/gaia/tree/master/shared/test
and create a marionette sub directory?