CI: Use dnf 2.0 for installation of packages in fedora
    
    Weak dependencies are intentionally disabled. If we need them
    then they should be explicitly specified because they are not weak.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/2809
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>