Bug 1024715 - Create test_firefox_accounts_login to validate user authen...

...tication from Settings and FMD R=zacc,bebe
Thanks, bebe.  I can certainly remove it if that's the case.  I only added it because Zac called it out here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1024715#c5
I was under the understanding he was suggesting I call this explicitly.  Since you've picked up the review from him, I can certainly remove it if you feel it's redundant.