Disable systemd-logind default power button handling to enable
pwr-button-handler service. 3 quick pushes of the power button
(3rd button from the left marked as PWR) makes the LED blink fast
and enables bluetooth pairing without further intervention.
Some devices (computer / laptop) require pairing using a PIN,
where the PIN consists of the last 6 digits from the serial number.
Other devices (phones) may pair without PIN.
Pairing while having Bluetooth tethering enabled will create a
bluetooth connection in connman.

Signed-off-by: Ferry Toth <ftoth@exalondelft.nl>