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

molecule/README.md

@@ -8,6 +8,9 @@ We have these scenarios:
 
 - **default**:
   A 3 control + 2 worker node cluster based very closely on the [sample inventory](../inventory/sample/).
+- **ipv6**:
+  A cluster that is externally accessible via IPv6 ([more information](ipv6/README.md))
+  To save a bit of test time, this cluster is _not_ highly available, it consists of only one control and one worker node.
 - **single_node**:
   Very similar to the default scenario, but uses only a single node for all cluster functionality.
 
@@ -32,6 +35,7 @@ To set the subnet up for use with VirtualBox, please make sure that `/etc/vbox/n
 
 ```
 * 192.168.30.0/24
+* fdad:bad:ba55::/64
 ```
 
 ### Install Python dependencies