Tests: use 127.0.0.1 instead of localhost.

Name 'localhost' is ambiguous if ipv6 present on system.
diff --git a/smtp-greeting-delay.t b/smtp-greeting-delay.t
index eccc9c2..4ed5b68 100644
--- a/smtp-greeting-delay.t
+++ b/smtp-greeting-delay.t
@@ -32,11 +32,11 @@
 
 mail {
     proxy_pass_error_message  on;
-    auth_http  http://localhost:8080/mail/auth;
+    auth_http  http://127.0.0.1:8080/mail/auth;
     xclient    off;
 
     server {
-        listen     localhost:8025;
+        listen     127.0.0.1:8025;
         protocol   smtp;
         smtp_greeting_delay  100ms;
     }