Only consider host in 'k8s_cluster' when checking if ip is a cached fact (#11817)

This avoids spurious failure with 'localhost'.

It should also be more correct the inventory contains uncached hosts
which are not in `k8s_cluster` and therefore should not be Kubespray
business.

(We still use hostvars for uncached hosts, because it's easier to select
on 'ansible_default_ipv4' that way and does not change the end result)