tools/testbed: use IOTLAB_NODE=auto instead of auto-ssh
tools/testbed: use IOTLAB_NODE=auto instead of auto-ssh

This deprecates the use of IOTLAB_NODE=auto-ssh

OlegHahm/RIOT,jasonatran/RIOT,kaspar030/RIOT,kaspar030/RIOT,authmillenon/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,ant9000/RIOT,authmillenon/RIOT,ant9000/RIOT,miri64/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,kaspar030/RIOT,kaspar030/RIOT,authmillenon/RIOT,ant9000/RIOT,kYc0o/RIOT,kYc0o/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,miri64/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,authmillenon/RIOT