Machine API Controller reports 'MachineSet [..] doesn't specify "cluster.k8s.io/cluster-name" label, assuming nil cluster'

Issue

• For a MachineSet, the Machine API Controller reports the following message every minute in its logs:

  I0109 12:10:10.213578       1 controller.go:304] MachineSet "abc-eu-central-1a" in namespace "openshift-machine-api" doesn't specify "cluster.k8s.io/cluster-name" label, assuming nil cluster
  I0109 12:11:11.482262       1 controller.go:304] MachineSet "abc-eu-central-1b" in namespace "openshift-machine-api" doesn't specify "cluster.k8s.io/cluster-name" label, assuming nil cluster
  I0109 12:12:10.447327       1 controller.go:304] MachineSet "abc-eu-central-1c" in namespace "openshift-machine-api" doesn't specify "cluster.k8s.io/cluster-name" label, assuming nil cluster