Merge pull request #1886 from mozilla/issue-1884-web-channel-test-stall

fix(test): Ensure the web channel tests complete. r=vladikoff
fix(client): The Sync flow should not notify the browser of login after the signup confirmation poll completes.

The browser polls in the background for the status of the sign up completion itself, the client does not need to notify it of completion.

In addition, the /confirm screen should not transition to the /signup_complete screen, this causes a jerky UI.

fixes #1881