fix(test): Fix the 'Unexpected error' flash in the sign_in tests.

In `sign in verified with password that incorrectly has leading whitespace`,
the call to `FunctionalHelpers.visibleByQSA` was incorrectly made inside
of a function passed to a .then. This caused the tests to move on before
the tooltip was visible, which ultimately caused the test to complete
before the signin XHR request was complete. Selenium would start to unload
the page, which aborted the outstanding XHR request, which caused the `Unexpected error` message.

Fixed the call to `FunctionalHelpers.visibleByQSA` as well as ensure
the expected error message is displayed.

Finally, moved a couple of reset password related tests to reset_password.js

fixes #1875
Merge pull request #1910 from mozilla/issue-1875-unexpected-error

fix(test): Fix the 'Unexpected error' flash in the sign_in tests.