HAProxy support for multi clusters

[viccross]

Fixes #102

Breaks the previous monolithic haproxy.cfg into sections. Some of the configuration will now be generated on-the-fly by an Ansible playbook that:

• generates the required configuration files per cluster (a file with the cluster backends, and a file with the cluster IPs for use in the m-c-s ACL)
• updates haproxy.cfg with the details of the new frontends.

The dynamic include directory is added to the ExecStartPre in the systemd service file since significant configuration will be held there now.