tools/openocd: check OPENOCD_VERIFY after IMAGE_OFFSET is computed
tools/openocd: check OPENOCD_VERIFY after IMAGE_OFFSET is computed

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