vpnaas is neutron plugin introduced in the Openstack Havana release. This module is able to manage vpn connection via openswan. The 'master' branch of puppet-neutron module contains support for vpnaas, but it needs to be supported by packstack in a similar way as the LBAAS agent supported.
I don't think adding vpnaas is high on the priority list to add to packstack. It is something that should be covered by the puppet modules however, so that it can be deployed manually or by Foreman. I've moved the component here to openstack-puppet-modules. Once the work is done on the puppet modules, if someone wanted to contribute patches to have those puppet modules used by packstack I don't think anyone would object, but the core packstack team probably won't be taking that on directly with any high priority
puppet-neutron has support for the vpnaas service in the neutron::agents::vpnaas module, introduced in https://review.openstack.org/#/c/48028/ This support is included in the openstack-puppet-modules package.