No OpenHAB-ondra Bluetooth (BlueZ) access

[Martin Hagborg]

BlueZ OpenHAB addon/binding thing Status: "UNINITIALIZED - HANDLER_INITIALIZING_ERROR"

i found this remark in the openhab documentation of blueZ:
“Also note that the OS user needs to be a member of the “bluetooth” group of Linux in order to have the rights to access the BlueZ stack”
how does one add “the OS user” to the “bluetooth group” on ubuntu snappy core?

or does the openhap snap (snapcraft.yaml) have to associate/consumes/implement/use the bluetooth/bluez plug (as sugested by the cannonical snapcraft.yaml documentation: “When a plug is connected to one of these slots, the application will be granted the permissions specified for that interface”)?

Ubuntu Core 18 on Raspberry PI 3B