* use StrongSwan driver instead of OpenSwan since xenial does not even provide openswan packages anymore * start and enable strongswan service (needs to be verified for centos) * do not include ::l3_agent recipe in vpnaas recipe, since neutron-vpn-agent fully replaces neutron-l3-agent Change-Id: I81cd2e05273402e8db57f3ca5029fb4938bbfe29