This allows us to use SNI for actual host (e.g. routing) information. We
don't have the client cert yet so we can't look at that, so this
provides a way for us to convey the information needed to look up that
session's TLS stack.
Using SNI for hosts means we also run into the fact that we don't have
automatic agreement in terms of SANs. So when generating the certs we
now also pass worker address information to the function to be encoded
in the cert.
Finally, there is a change in how the websocket dialing happens, because
http.RoundTripper tries to be too clever for its own good and overwrites
NextProtos on a whim.
Jeff Mitchell
58a448fc6a