Disable OMPL's demos in moveit2 image (#228).

This commit disables OMPL's demos, due to a build error that results in a
header file not being found.

```
<PATH_TO_OMPL>/demos/DubinsAirplane.cpp:48:10: fatal error: ompl/tools/debug/Profiler.h: No such file or directory
   48 | #include <ompl/tools/debug/Profiler.h>
```

Author: ivanperez-keera

moveit2/Dockerfile

@@ -129,8 +129,10 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
  && rosdep install --from-paths src --ignore-src --rosdistro ${ROS_DISTRO} -r -y --skip-keys \"$(cat /tmp/rosdep-skip.txt | tr '\n' ' ')\""
 
 # Build MoveIt2
+#
+# We temporarily disable OMPL's demos due to a build error.
 RUN /bin/bash -c 'source ${SPACEROS_DIR}/install/setup.bash \
-  && colcon build --cmake-args -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=ON --event-handlers desktop_notification- status-'
+  && colcon build --cmake-args -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DOMPL_BUILD_DEMOS=OFF --event-handlers desktop_notification- status-'
 
 # Add a couple sample GUI apps for testing
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \