message: add smoothie id environment variable
diff: # Use this for running on a robot
  FROM resin/raspberrypi3-alpine-python:3.6-slim
  -ENV RUNNING_ON_PI 1
  +ENV RUNNING_ON_PI=1
  ENV DBUS_SYSTEM_BUS_ADDRESS=unix:path=/host/run/dbus/system_bus_socket
  -ENV PYTHONPATH $PYTHONPATH:/data/packages/usr/local/lib/python3.6/site-packages
  +ENV PYTHONPATH=$PYTHONPATH:/data/packages/usr/local/lib/python3.6/site-packages
  +#port name for connecting to smoothie over serial
  +ENV OT_SMOOTHIE_ID=AMA
  RUN echo "export DBUS_SYSTEM_BUS_ADDRESS=$DBUS_SYSTEM_BUS_ADDRESS" >> /etc/profile && \
  echo "export PYTHONPATH=$PYTHONPATH" >> /etc/profile && \
  