fix(client): Ensure auth-server errors are displayed on confirm pages.

* submit returns a promise, and this is used to simplify the tests.

fixes #843
fixes #844
fix(tests): Update unit and functional tests to handle throttled password reset email requests.

* Merge all reset password related functional tests into one file that tests the full flow.

fixes #842
Merge pull request #850 from mozilla/issue-842-throttle-resend-tests

fix(tests): Update unit and functional tests to handle throttled password reset email requests.
fix(client): transition from password reset confirmation to signin once reset is complete
fix(tests): Ensure enough test coverage for confirm_reset_password.