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.
The test tries to detect the presence of pavucontrol's
window by looking for the tab label "Playback".
However, the OCR mechanism fails to resolve the
text, possibly due to the grey background color.
To fix this issue, we instead look for the name of the
sound device ("Dummy Output") which gets resolved by OCR.
Note: Strangely, the tab "Playback" *is* correctly
resolved when the test is run in interactive mode.
This might be due to the changed screen resolution,
but I didn't investigate further.
