Only set special_service_provider on RHEL.

Updates the params.pp so that special_service_provider is set
to 'init' on RHEL only. This gets used to startup libvirtd.

This fixes issues using the Nova compute/libvirt module on
Fedora.

Change-Id: I81f6a50a10f8e16e5d54b93724258a977c35d61f
Merge "Only set special_service_provider on RHEL."