tests: dual-proto: Fail gracefully on firewall
tests: dual-proto: Fail gracefully on firewall

* Firewall was already configured, don't exit the unit test.

elie195/docker-openvpn,hjnijlunsing/docker-openvpn-armhf,slamont/docker-openvpn,kylemanna/docker-openvpn,myplacedk/docker-openvpn