Optionally manage node networking with ansible:

- write `network_interfaces` var to /etc/network/interfaces, if defined.
  this is very useful on network nodes, where iptables rules, floatingips,
  etc. must be defined.

- set /etc/hosts entries from var `etc_hosts` to allow for static lookup
  when DNS is not available.
  e.g.
    etc_hosts:
      - name: controller.example.com
        ip: 1.2.3.4