testing: Load kdf plugin in all scenarios that require it

Once we use plugin-provided prf+() these won't work otherwise.

testing/hosts/bob/etc/strongswan.conf

@@ -1,5 +1,5 @@
 # /etc/strongswan.conf - strongSwan configuration file
 
 charon {
-  load = sha1 sha2 md5 aes des hmac pem pkcs1 x509 revocation constraints curve25519 pubkey gmp random nonce curl kernel-netlink socket-default updown stroke vici
+  load = sha1 sha2 md5 aes des hmac kdf pem pkcs1 x509 revocation constraints curve25519 pubkey gmp random nonce curl kernel-netlink socket-default updown stroke vici
 }