Add tests for containerized Mock

[praiskup]

The whole TF test suite is being run against the fedora-latest-x86_64 VM.

Sometimes it would be nice to test Mock's behavior on different systems, and we don't necessarily have to go with different VM, a container would be just enough.

I think we need

1. start another F40 VM
2. build a container image with the target system (e.g. c9s), we may need a matrix of images, and we need to install the appropriate package version from the right pull-request commit (or from pushed commit)
3. test the mock image ^^^ with podman run --privileged