Added a python-pyrss2gen package resource to openstackwatch.pp.

Change-Id: I556af39abb0446acac19381edc855172e22bdfa8
Reviewed-on: https://review.openstack.org/24607
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins