ubuntu.py: update to dual install to Python2

[hamishwillee]

The current build depends on some Python 2; this just adds all python 2 depdendencies to the "user build script".

Note is WIP. Jmavsim works, but Gazebo (9) isn't starting on ubuntu 16.04. More testing required.

[hamishwillee]

Gazebo fails with this build log after setting up env with this file.

EDITED: I updated the gazebo section to include everything in docker. The minimum to start gazebo is much smaller (protobuf-compiler libeigen3-dev libopencv-dev gazebo9 libgazebo9-dev) but I am assuming you need the rest for video simulation.

[julianoes]

I'm opposed to this change. I would rather have everything properly changed to Python3.

I have been building PX4 for years on systems with Python3 as the default, so I want to understand why that would not work.

[hamishwillee]

@julianoes So would I. But are you happy to urgently commit the time to working out how to do it?

At the moment there is no working mechanism for automated environment setup on ubuntu. Getting this out there and allowing easy setup is more important than "general principle".

[hamishwillee]

Note, getting some warnings:

Successfully installed pip-19.2.3 setuptools-41.2.0 wheel-0.33.6
WARNING: The directory '/home/ubuntu/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
WARNING: The directory '/home/ubuntu/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.

[julianoes]

@hamishwillee alright here #12809.

[hamishwillee]

@julianoes You're my hero :-). I'll close this once that goes in and I can retest.

[julianoes]

@hamishwillee maybe will need this as an intermediate step. Python 3 everywhere isn't trivial I had to find out.

[hamishwillee]

@julianoes OK, can you or @dagar approve the merge then?

[hamishwillee]

@dagar Thanks. Is this in CI yet too? If not, any clues/pointers to similar things that I might copy to get it in.

Basically I want to make sure that this can be used to set up an env that builds jmavsim, gazebo and nuttx. Ideally also tests that the SIMs run successfully.