DNF is used on CentOS CI by default

Hi all, I now noticed that at least in [1], otopi found and used DNF on CentOS. Meaning, we install at least enough of dnf there to make otopi be able to use it. Was this done on purpose? Or is this an unplanned result of a recent upgrade? Something else? [1] https://jenkins.ovirt.org/job/otopi_master_check-patch-el7-x86_64/506/ -- Didi