Use requirements.txt and requirements-test.txt to organize better Python
dependencies related to LAVA.
Now LAVA tooling can use recent and fixed library versions.
And test-related libs will not trigger container rebuilding anymore.
Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21325>