ros python to python3 conversion

[Scott Kitterman]

Note: Please cc me on any replies, I am not subscribed.

Dear Debian Science,

As many of you know, we are working on getting rid of python2 in this 
development cycle and either moving packages to python3 or removing them.  
It's a large effort (around 4K packages affected) [1].  If you look at our 
removal tracker, many of the ros packages are near the top of the dependency 
stack, which means they block other python2 removals.

I took a brief look at python3 support in ros, and as far as I can tell, it 
appears to be python3 ready, it just needs someone to change it over.  Since 
it seems like there are multiple packages involved, I would appreciate it if 
someone in debian-science would have a look and see about changing it over.  I 
started with python-rviz and got confused from there.

Thanks,

Scott K

[1] https://release.debian.org/transitions/html/python2-rm.html