Enable VPN as a Service

The current rendition of puppet_openstack_builder doesn't show users how to set up their cloud to use Neutron's VPN as a Service feature. Due to previous work done to enable LBaaS, this should be a pretty straightforward matter of adding a couple of data mappings and settings in user.common.yaml. Note that the StackForge classes for LBaaS feature a package_ensure parameter (not all other do), so we should map that as well.