Podman support in functional tests

Improve container support in tox.ini

Podman.io is a rootless and serverless alternative to Docker.io.
It avoids using sudo in many cases, what is a good thing.
It is now prefered to Docker.io by many linux distributions.[

https://podman.io/] https://access.redhat.com/solutions/3696691
https://thesynack.com/posts/docker-compose-podman/
https://martinheinz.dev/blog/35