RFC 7427: pluto (responder) impaired to not see strongswan's (initiator) SIGNATURE_HASH_ALGORITHMS

Check that pluto will prove its identity using legacy RSA when the
initiator doesn't send SIGNATURE_HASH_ALGORITHMS.

Basic pluto with IKEv2 using X.509 on the responder (east), and
Strongswan on the initiator (west).

Responder's proof-of-identity uses RSA-SHA1 (old style RSA).

Initiator's proof-of-identity uses Digital Signature Method (since
pluto always sends its hash algorithms).

