According to pulseaudio(1), a system wide pulseaudio instance
can only be accessed by members of the `pulse-access` group.
This name seems to be hardcoded in
pulseaudio -- I didn't find any switch to change it.
We need to define the group so users can connect to the deamon.
This commit also fixes the systemwide pulseaudio vm test:
Previously, the test user `alice`
was just a member of the `audio` group.
This blocked access to the daemon and failed the test.
The commit changes the group assignment and fixes the vm test.