dist/tools/kconfiglib: Use python3 for RIOT adaption of menuconfig
dist/tools/kconfiglib: Use python3 for RIOT adaption of menuconfig

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