Before, a fallback http server was created to handle requests for
unknown virtual hosts even when `HTTPS_METHOD=nohttp`. (In this case,
all http vhosts would be unknown.) Likewise, a catch-all fallback
https server was still created even if `HTTPS_METHOD=nohttps`.
Now the fallback servers are created only if needed. This brings the
behavior in line with the documentation and user expectation. It will
also make it easier to implement a planned feature: different servers
on different ports.
