If you cannot start a cluster and see that error in the logs it most likely means that AppArmor is running on your server and is preventing Vitess processes from accessing the my.cnf file.
The workaround is to uninstall AppArmor:
sudo service apparmor stop sudo service apparmor teardown sudo update-rc.d -f apparmor remove
You may also need to reboot the machine after this. Many programs automatically install AppArmor, so you may need to uninstall again.