v2: Verbatim translation from the original shell script
    Make the corrections visible in explicit commits (Andres)
    Remove redundant code (Alexandros)
    Code style nitpick (Rohan)

Reimplementation of the tracie's self-tests using a pythonic test suit
(pytest).

The new tracie/test.py module is almost a direct translation of the
tests defined in the tracie/test.sh. This new implementation of the
test provides a more common framework where define the tests.
Also allows a better introspection for the tests results and/or
resulting errors.

This patch also adds python3-pytest as dependency for the built images
and adapts the tracie-runner scripts to run the self-test using pytest.

Signed-off-by: Pablo Saavedra <psaavedra@igalia.com>
Reviewed-by: Alexandros Frantzis <alexandros.frantzis@collabora.com> [v1]
Reviewed-by: Andres Gomez <agomez@igalia.com>
Reviewed-by: Rohan Garg <rohan.garg@collabora.com> [v1]
Part-of: <!4916>