Added an IPv6 check

Playbook fails with propper error msg if IPv6 is enabled but not
available.

ansible/roles/openshift-4-cluster/tasks/create-network.yml

@@ -4,6 +4,13 @@
 #     src: templates/network.xml.j2
 #     dest: network.xml
 
+- name: Check IPv6
+  fail:
+    msg: "IPv6 is enabled via ip_families but your Host system do not have a public IPv6 subnet configured."
+  when:
+    - "'IPv6' in ip_families"
+    - hostvars['localhost']['ansible_default_ipv6'] | length == 0
+
 - name: Build IPv6 subnet
   set_fact:
     vn_subnet_ipv6: "{{ hostvars['localhost']['ansible_default_ipv6']['address'].split(':')[:4] | join(':') | string}}:{{ '%x' % vn_subnet.split('.')[2] | int }}"