[Dovecot] director with multiple instances

[Will Yardley]

And I realize that doveadm isn't setup properly yet, and that
director_doveadm_port needs to be doveadm's inet_listener, not
director's as it is now. Presumably this should just affect being able
to run doveadm, though, and not cause the problems I mentioned?

It would be really convenient if running the directors and backend
services on the same set of machines was a lot easier out of the box.
Especially being able to configure a static mapping of listener =>
backend port without having to do a fake SQL map would really simplify
things.

w