Enable dual stack IPv4 and IPv6 VIPs on the same interface.
HAProxy always listens on both IPv4 and IPv6 allowing connectivity
on either protocol.

Update edge cases for is_ssl_cert_master for Bug #1709356.

Update amulet tests for keystoneauth1 tests.

charm-helpers sync for HAProxy template changes.

Closes-Bug: #1709356

Change-Id: I401071fcdd66252f389475d45e8136fc68c474f1