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

This test enables --impair-minor-version-bump that will send a higher
minor version number on the responder. The connection should still
establish fine.

See: https://tools.ietf.org/html/rfc5996#section-2.5

   The major version number should be incremented only if the packet
   formats or required actions have changed so dramatically that an
   older version node would not be able to interoperate with a newer
   version node if it simply ignored the fields it did not understand
   and took the actions specified in the older specification.  The minor
   version number indicates new capabilities, and MUST be ignored by a
   node with a smaller minor version number, but used for informational
   purposes by the node with the larger minor version number.  For
   example, it might indicate the ability to process a newly defined
   Notify message type.  The node with the larger minor version number
   would simply note that its correspondent would not be able to
   understand that message and therefore would not send it.