RequireHttpsAttribute doesn't change the port

[Tratcher]

RequireHttpsAttribute changes the scheme but not the port, so http://localhost:44380/ gets redirected to https://localhost:44380/, which is invalid because you can't serve both http and https on the same port.

The only way this ever worked was if the original request's host header did not include the port (e.g. localhost rather than localhost:80)

There's even a (wrong) test:
25838ce#diff-ba666c0ff94ddf047b6f11caa0ac94c9R42

@sebastienros @blowdart @javiercn

[Eilon]

Kind of related to #4093

In the default case we should indeed drop the port number when redirecting to HTTPS, and fix the offending test.