Advanced Firewalling feature

This patch enables Firewalling in this Puppet modules in a flexible way.

* Enable firewalling optionnaly (disabled by default).
* Enable 'pre' firewalling with defaults rules.
* Enable 'post' firewalling with DROP rule, with a debug option to
  disable it.
* Enable default rules for all services (OpenStack, etc).
* Ability to add custom firewall rules with Hiera
* Update puppetlabs-firewall refs
* Refactorize unit-tests
```firewall_settings``` could be a hash with the service name as the key for the settings for each service … and eventually a ```__GLOBAL__``` key with general settings to be overloaded by each service settings ?