testing: Add ikev2/rw-sig-auth scenario

testing/tests/ikev2/rw-sig-auth/hosts/dave/etc/strongswan.conf

@@ -0,0 +1,5 @@
+# /etc/strongswan.conf - strongSwan configuration file
+
+charon {
+  load = aes des sha1 sha2 md5 pem pkcs1 gmp random nonce x509 curl revocation hmac xcbc stroke kernel-netlink socket-default fips-prf updown
+}