Basic pluto with IKEv1 using PSK on the responder (east), and Strongswan on
the initiator (west).

This tests our response to DH22, which we no longer support. This is using IKEv2.
Unlike IKEv1, stongswan now does allow us to use DH24, and the connection succeeds
with DH24 after libreswan rejects DH22
