Remove serialized collect of ansible_default_ipv4

The fallback_ips tasks are essentially serializing the gathering of one
fact on all the hosts, which can have dramatic performance implications
on large clusters (several minutes).

This is essentially a reversal of 35f248dff0
Being able to run without refreshing the cache facts is not worth it.

We keep fallback_ip for now, simply changing the access to a normal
hostvars variable instead of a custom dictionnary.

roles/kubernetes/control-plane/tasks/kubeadm-upgrade.yml

@@ -1,7 +1,7 @@
 ---
 - name: Kubeadm | Check api is up
   uri:
-    url: "https://{{ ip | default(fallback_ips[inventory_hostname]) }}:{{ kube_apiserver_port }}/healthz"
+    url: "https://{{ ip | default(fallback_ip) }}:{{ kube_apiserver_port }}/healthz"
     validate_certs: false
   when: ('kube_control_plane' in group_names)
   register: _result