RPi testing and fixes

[BenGardiner]

lots of little details I missed out on in trying to create separate users for each device/session.

Plus one change (at least) that might be unexpected. On this RPI I can't get tmate sessions to run under systemd unless -F is supplied. This is the same with upstart on the truck duck.

On RPi here without -F systemctl status -l reports:

pi@raspberrypi:~/src/HardwareCheckout $ sudo systemctl status session@device0.service
● session@device0.service - Starts tmate session
   Loaded: loaded (/etc/systemd/system/session@.service; disabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Tue 2020-08-04 06:14:20 BST; 15s ago
  Process: 2813 ExecStartPre=/usr/bin/install -m 777 -d /tmp/devices (code=exited, status=0/SUCCESS)
  Process: 2817 ExecStartPre=/bin/su villager-device0 -c install -m 700 -d /tmp/devices/device0 (code=exited, status=0/SUCCESS)
  Process: 2926 ExecStartPre=/usr/bin/pkill -9 -u villager-device0 (code=exited, status=0/SUCCESS)
  Process: 2927 ExecStart=/bin/su villager-device0 -c /usr/bin/tmate -S /tmp/devices/device0/device0.sock new-session (code=exited, status=1/
 Main PID: 2927 (code=exited, status=1/FAILURE)

Aug 04 06:14:20 raspberrypi systemd[1]: session@device0.service: Service RestartSec=100ms expired, scheduling restart.
Aug 04 06:14:20 raspberrypi systemd[1]: session@device0.service: Scheduled restart job, restart counter is at 5.
Aug 04 06:14:20 raspberrypi systemd[1]: Stopped Starts tmate session.
Aug 04 06:14:20 raspberrypi systemd[1]: session@device0.service: Start request repeated too quickly.
Aug 04 06:14:20 raspberrypi systemd[1]: session@device0.service: Failed with result 'exit-code'.
Aug 04 06:14:20 raspberrypi systemd[1]: Failed to start Starts tmate session.