testnode: Make sure PowerTools repo is enabled on CentOS
https://github.com/ceph/ceph-cm-ansible/pull/731 removed the
custom-made repo files that added mirrorlists; however, it also
removed the side-effect of enabling the Power Tools repo (which
is not enabled by default). This adds a call to dnf config-manager
to enable the repo, whatever its repo file name, on CentOS
testnodes.
Fixes: https://tracker.ceph.com/issues/59678 Signed-off-by: Dan Mick <dmick@redhat.com>