Fix PulseAudio tunnelling for server running on host, outside network namespace

[jamesmcm]

See https://wiki.archlinux.org/index.php/PulseAudio#On_the_server

Need to forward TCP port 4713 from host in to network namespace, and then set the host to be the Pulse Audio server address (i.e. 10.200.1.1).

Ideally we'd proxy localhost:4713 inside the namespace to the host address to avoid dealing with setting environment variables every time, but then we need a way of running the TCP proxy inside the namespace itself (currently we run it as part of vopono on the host, outside the namespace).

[jamesmcm]

Same applies to D-Bus.

[jamesmcm]

For PulseAudio don't need networking, can use:

PULSE_SERVER="/run/user/1000/pulse/native"

and pass through to all commands with sudo -E both in netns invocation and the command invocation.

Get string from pactl info on host.

[jamesmcm]

Fixed in #44