Tests: implement smtp test backend and use it.
diff --git a/smtp-greeting-delay.t b/smtp-greeting-delay.t
index 06181e5..2c09401 100644
--- a/smtp-greeting-delay.t
+++ b/smtp-greeting-delay.t
@@ -38,7 +38,7 @@
     xclient    off;
 
     server {
-        listen     localhost:10025;
+        listen     localhost:8025;
         protocol   smtp;
         smtp_greeting_delay  100ms;
     }