openstacklib::policy has never been used in any other modules because
it was implemented as a class not reusable for each service.
This change re-implements openstacklib::policy as a defined resource
type so that we can use this implementation from each puppet modules.
The openstacklib::policy resource type provides the purge_config
parameter. When this parameter is set to true, a policy file is cleared
during configuration process. This allows users to remove any existing
rules before applying their own (no) rules.
Change-Id: I9bb486c9191c50c11717dcb9c6af00d17c3aa8f5
2a53c66ed3