Add fedora18 and fedora18-dev slaves.

* manifests/site.pp: Add node name patterns for fedora18 production
and development slaves with Python 3 support switched on.

Change-Id: I7eac41e6dccde50be962cbc3fda21ac90c3d246b
Reviewed-on: https://review.openstack.org/34084
Reviewed-by: Dan Prince <dprince@redhat.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins