Bug 1096824 - [Loop] Sign up requests might be unauthorized due to assertions expired

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1096824. Action happens at https://github.com/jaoo/firefoxos-loop-client/tree/1096824.
> I'm not that sure this will fix the problem... If the signin can also send a expired error then we're > not controlling that case (which might be the actual problem we're running into). Also, if there's a > sign in error, we should try to do a signup (with the assertion we already have) before failing with > the onlogin error

Actually we are taking care of the 401/110 error during the sign in proccess (see https://github.com/mozilla-b2g/firefoxos-loop-client/blob/master/app/js/helpers/account_helper.js#L471) however the flow to follow in that case is to inform the user and logout as we agree with UX folks.