added two scenarios testing repeated authentication (RFC 4478)

testing/tests/ikev2/reauth-early/description.txt

@@ -0,0 +1,7 @@
+This scenario tests <b>repeated authentication</b> according to RFC 4478.
+The iniator <b>carol</b> sets a large <b>ikelifetime=20m</b> but the responder
+<b>moon</b> defining a much shorter <b>ikelifetime=30s</b> proposes this
+value via an AUTH_LIFETIME notification to the initiator. Thus the 
+IKE reauthentication takes places after less than 30s. A ping from
+<b>carol</b> to client <b>alice</b> hiding in the subnet behind <b>moon</b>
+tests if the CHILD_SA has been inherited by the new IKE_SA.