Add support for API servers on IPv6 addresses (#48)

* Remove duplicate file for deletion

* Add support for IPv6 clusters

To correctly escape IPv6 addresses when ports are used, they must be
wrapped in square brackets [1]. This patch adds support for that,
using Ansible's ipwrap filter [2].

[1]: https://datatracker.ietf.org/doc/html/rfc4038#section-5.1
[2]: http://docs.ansible.com/ansible/latest/collections/ansible/utils/docsite/filters_ipaddr.html#wrapping-ipv6-addresses-in-brackets

* Do not abort other molecule jobs on failure

* Fix cache keys for Vagrant boxes

* Molecule: Derive overrides.yml location from scenario dir

# Conflicts:
#	molecule/default/molecule.yml
#	molecule/ipv6/molecule.yml

roles/prereq/tasks/main.yml

@@ -23,6 +23,13 @@
     state: present
     reload: yes
 
+- name: Enable IPv6 router advertisements
+  sysctl:
+    name: net.ipv6.conf.all.accept_ra
+    value: "2"
+    state: present
+    reload: yes
+
 - name: Add br_netfilter to /etc/modules-load.d/
   copy:
     content: "br_netfilter"