make sure that systemd of rpiblutooth stays alive

[dogi]

... and recovers when crashed

root@r135rpi8:~# date
Thu 18 Jun 01:47:36 UTC 2020
root@r135rpi8:~# service rpibluetooth status
● rpibluetooth.service - Bluetooth server
   Loaded: loaded (/etc/systemd/system/rpibluetooth.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Mon 2020-06-15 01:17:19 UTC; 3 days ago
  Process: 411 ExecStart=/usr/bin/python3 /usr/local/bin/bluetooth-server.py & (code=exited, status=1/FAILURE)
 Main PID: 411 (code=exited, status=1/FAILURE)

Jun 15 01:17:19 r135rpi8 python3[411]:     multithreaded_server.run()
Jun 15 01:17:19 r135rpi8 python3[411]:   File "/usr/local/bin/bluetooth-server.py", line 136, in run
Jun 15 01:17:19 r135rpi8 python3[411]:     self.advertise_service()
Jun 15 01:17:19 r135rpi8 python3[411]:   File "/usr/local/bin/bluetooth-server.py", line 109, in advertise_service
Jun 15 01:17:19 r135rpi8 python3[411]:     profiles=[bluetooth.SERIAL_PORT_PROFILE])
Jun 15 01:17:19 r135rpi8 python3[411]:   File "/usr/local/lib/python3.7/dist-packages/bluetooth/bluez.py", line 275, in advertise_service
Jun 15 01:17:19 r135rpi8 python3[411]:     raise BluetoothError (*e.args)
Jun 15 01:17:19 r135rpi8 python3[411]: bluetooth.btcommon.BluetoothError: no advertisable device
Jun 15 01:17:19 r135rpi8 systemd[1]: rpibluetooth.service: Main process exited, code=exited, status=1/FAILURE
Jun 15 01:17:19 r135rpi8 systemd[1]: rpibluetooth.service: Failed with result 'exit-code'.
root@r135rpi8:~# treehouses bluetooth button
ok. button enabled