akraino/validation:os-latest is missing python

https://gerrit.akraino.org/r/c/validation/+/1863 introduced a defect on the generated docker image.

python was missing. python supposed to run pyton3 on this image.

python3 is also not not working and reporting following

This system supports the C.UTF-8 locale which is recommended.
You might be able to resolve your issue by exporting the
following environment variables:

export LC_ALL=C.UTF-8
export LANG=C.UTF-8