Add default values to ARGs

dockerfiles/devenv.Dockerfile

 ARG ROS_DISTRO
 FROM osrf/ros:${ROS_DISTRO}-desktop-full
 
-ARG EXT_SHELL
+ARG EXT_SHELL=bash
 RUN echo "Building devenv for ROS" $ROS_DISTRO "with shell" $EXT_SHELL
 
 # Avoid warnings by switching to noninteractive
@@ -125,7 +125,7 @@ RUN rm -rf *
 
 RUN apt-get --reinstall install -y libnotify-bin notify-osd
 
-ARG PEAK_DRIVER=install
+ARG PEAK_DRIVER=none
 RUN if [ "$PEAK_DRIVER" = "install" ]; \
     then \
     apt-get update && apt-get install -y udev libpopt-dev linux-headers-$(uname -r) \
@@ -166,7 +166,7 @@ ENV DEBIAN_FRONTEND=
 ENV ROS_LOCALHOST_ONLY=1
 ENV RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
 
-ARG SHELL
+ARG SHELL=/bin/bash
 ENV SHELL="${SHELL}"
 
 ENTRYPOINT ["/ros_entrypoint.sh"]