This closes #69 and #80 with the following error:
*** No rule to make target `/usr/lib/genpy/genmsg_py.py', needed by
`devel/lib/python2.7/site-packages/std_msgs/msg/_Bool.py'.  Stop.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

The python binary path for genmsg_py.py and gensrv_py.py are hard
coded in the CMake file and don't work during cross compile. Setup
them via find_program during runtime.

This fix #69 and the following error:
*** No rule to make target `/usr/lib/genpy/genmsg_py.py', needed by
`devel/lib/python2.7/site-packages/std_msgs/msg/_Bool.py'.  Stop.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

When importing the rosbag module in python, it fails in a genpy python module
complaining about missing the shutil python module. The shutils module is
provided by python-shell.

All ROS packages with install tools in the bin directory or install
python code with is used by other packages should be used as native
version. Adapte the DEPENDS accordingly.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>