First run:
sudo -u openhab ls
from a terminal. This will let you acknowledge and get rid of that message. It only appears the first time you run sudo as a given user.
Second, adding openhab to the sudo group may not be enough because you also have to configure it so the openhab user does not have to enter a password to run sudo commands.
Do you have to run the command with sudo when running it as a regular user? If not then there is some other group that your regular user belongs to that needs to be added to the openhab user. I have no idea what resources these command access or how they work so you will have to figure that part out. You should run these commands as root through sudo only as a last resort.
Finally, if you do have to run it as sudo, then you should user your shell script and put the sudo before the call to your shell script.