2794.change

The little-used "control port" now uses a separate (ephemeral) Tub. This
means the FURL changes each time the node is restarted, and it only listens
on the loopback (127.0.0.1) interface, on a random port. As the control port
is only used by some automated tests (check_memory, check_speed), this
shouldn't affect anyone.

The slightly-more-used "log port" now also uses a separate (ephemeral) Tub,
with the same consequences. The lack of a stable (and externally-reachable)
logport.furl means it is no longer possible to use `flogtool tail FURL`
against a distant Tahoe server, however `flogtool tail
.../nodedir/private/logport.furl` still works just fine (and is the more
common use case anyways). We might bring back the ability to configure the
port and location of the logport in the future, if there is sufficient
demand, but for now it seems better to avoid the complexity.