As of Queens the VPNaaS package to be used is no longer
neutron-vpn-agent and has been replaced with the package
python-neutron-vpnaas.
The package for openswan does not exist for Debian systems
and needs to be updated to strongswan instead.
Change-Id: I859c80facc9dadf461c2300a6c354c73ae60e5e4
Closes-bug: #1825700