Add a Dockerfile for building testing image
    
    When migrating to a new jenkins instance, we found some packages
    are missing in the new jenkins nodes, using the image we can run
    tests easily without installing those dependencies.
    
    podman build -t cts-test -f tests/Dockerfile-test .
    
    podman run --rm -v .:/src:Z cts-test
    
    JIRA: RHELCMP-4580