An interop test of Authenticated Header (AH) using sha2_512

This uses IKEv1. It requires xfrm

This test requires strongswan 5.1.1 or newer for AH support.

This test doesn't work with strongswan 5.5.1 .. 5.5.3 see
https://wiki.strongswan.org/issues/2347.

Due to a strongswan bug in 5.6.0, we have to disable PFS because
strongswan seems to never allow PFS for AH based connections.
