This change adds a custom fact called os_service_default, for use with
the openstack modules to provide the '<SERVICE DEFAULT>' string for
configurations.
Static external facts can be loaded from <MODULEPATH>/<MODULE>/facts.d/
starting with Puppet 3.4/Facter 2.0.1. Prior to this change, the static
facts needed to be placed in an environment specific location. For
Facter < 2.0.1, we are providing a regular ruby fact.
Change-Id: Id6eec6f96d545bb0054aad30bf359cf32521c83a