Fix empty kube_override_hostname in apiserver_sans (#4916)
Fix empty kube_override_hostname in apiserver_sans (#4916)

kubernetes/master role defines this value as an empty string
when using a cloud provider, not undefined. The check was updated
accordingly.

Change-Id: I58dc31ef4fd568a717a6753eb89ca687933018ae
kubernetes-incubator/kargo,kubernetes-incubator/kubespray,Atoms/kubespray,kubernetes-incubator/kubespray,kubernetes-incubator/kargo,kubernetes-sigs/kubespray,kubernetes-sigs/kubespray,Atoms/kubespray,kubernetes-sigs/kubespray,Atoms/kubespray,kubernetes-sigs/kubespray,Atoms/kubespray