Since python 3.3, the recommended way to setup a virtual env is
via "python -m venv".

Set this as a default, if python version is compatible with
such feature.

While here, add more comments to it, as the script is
getting more complex. So, better to add more things, to avoid
accidentally breaking it while improving it.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/252cc849c79527ad496247e4c481961478adf41c.1586883286.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>