Investigate and fix Python 3 dependency

[Georacer]

Currently, ROS Kinetic has a Python 3 dependency and inclusion.
However, MAVProxy works with Python 2.X and breaks on call of some modules e.g. map.

To call arduplane SITL properly, you must call the sim_vehicle.py from a shell that sees Python 2.X but then raise the last_letter simulation after exporting ROS workspaces.