virtual-stb: Add run a fake-lircd in the virtual stb to inject key events

Allows customising the mapping between the keycode names that stbt sees and
the XKeySyms that X and the program under test understands.
Dockerfile: Load config file from tests repo
service: The system configuration should come from the host
service: Use the volumes from the virtual-stb
virtual-stb: Attempt to fix volumes