fix(test): Fix `test-latest` functional tests when clearing browser state and when loading emails.

@vladikoff - could you review this? There were two problems. The first is, if the content server was not already loaded when trying to clear state, the tests would error out because pages load slowly when loaded off of remote servers. The second is, the number of the email we were looking for was not being passed to restmail. As long as one email was available for the user, restmail would return the lone email, even if we wanted the second.

fixes #1690