fallback_ips: ignore unreachable hosts (#10601)

Sets ignore_unreachable: true to `Gather ansible_default_ipv4 from all hosts`
task from fallback_ips.yml

Without this scale.yml will fail if a single node in the cluster is down, which
for large clusters happens often.

roles/kubespray-defaults/tasks/fallback_ips.yml

@@ -12,6 +12,7 @@
   when: hostvars[item].ansible_default_ipv4 is not defined
   loop: "{{ (groups['k8s_cluster'] | default([]) + groups['etcd'] | default([]) + groups['calico_rr'] | default([])) | unique }}"
   run_once: yes
+  ignore_unreachable: true
   tags: always
 
 - name: Create fallback_ips_base