Don't attempt to send beta labs errors/fatals to vanadium

This patch uses a template variable to set a different target for
fatals/exceptions depending on the realm. I don't really like the whole
'template_variables' param thing that misc::udp2log::instance is doing, but
that's how it was written.

Change-Id: Ia0cc8de4399a29119e3d572f0dd8ef43424700ac