@kyrofa is correct , using /dev/ttyUSB* does not work.
2018-02-27T07:37:13Z INFO snap "pc" has bad plugs or slots: usb0, usb1, usb2, usb3 (serial-port path attribute specifies invalid symlink location)
Anyhow the original question still is open (how to add user to dialout group)
I found this being suggested in another forum topic.