Windows builds failing in Travis due to Python 2.x

[vladak]

Windows builds have started failing couple of days ago in the python venv generate for opengrok tools (saying it does not know the venv module). This is due to the fact that default python executable is 2.7.9 (verified by replacing venv step with python -V).

[vladak]

As the most recent (5 months ago) comment on https://chocolatey.org/packages/python3#install says:

This package should also add python3 to PATH, but when installing it the only available commands are python and pip, and pip3. This causes shebangs used on Linux such as #!/usr/bin/env python3 to not work on Windows. The Python on Microsoft Store does that.

[vladak]

This is caused by Chocolatey switch to Python 3.9 so the PATH no longer has a valid Python 3.x version.