fix(tests): Fix the oauth_webchannel tests when run by themselves.

@vladikoff - could you review this?

In beforeEach, FunctionalHelpers.clearBrowserState was being called before any page was loaded, meaning localStorage and sessionStorage were not being cleared for the content server. This has the side effect that the tests contained a subtle bug where they unknowingly depended on other tests to sign a user in.

The fix is to load the content server's page before running FunctionalHelpers.clearBrowserState.

fixes #1669 

I understand the concern, my thoughts is that I'd rather it be correct, all the time, than super speedy.

The stats while running functional tests excluding oauth: 
without: npm run-script test-functional  3.35s user 0.64s system 3% cpu 2:01.84 total
with: npm run-script test-functional  3.56s user 0.69s system 2% cpu 2:27.38 total

including oauth:
without: npm run-script test-functional  3.86s user 0.76s system 3% cpu 2:28.53 total
with: npm run-script test-functional  4.12s user 0.82s system 2% cpu 2:55.59 total