Basic pluto with IKEv2 using PSK on the initiator (west), and Strongswan on
the responder.

This uses  ike and esp values of aes128-sha1 on both sides.

older versions of libreswan did not send a keysize for ike=aes-sha1 and
required ike=aes128-sha1 for interop. We now specifically use ike=aes-sha1
on the libreswan end to test conformance of KEY_LENGTH sending.

note libreswan also used to use aes256 when specifying esp=aes-sha1. This
has been changed to aes128 as that is the only mandatory to implement
key size as per RFC 3602. This also matches other implementations such as
strongswan.