Use localhost to test IPv6 connectivity

.vsftpd.conf

@@ -1,6 +1,8 @@
 # Used by Travis CI
 
-listen=YES
+listen=NO
+listen_ipv6=YES
+
 write_enable=YES
 dirmessage_enable=YES
 secure_chroot_dir=/var/run/vsftpd/empty

client_test.go

@@ -151,7 +151,7 @@ func TestConnIPv6(t *testing.T) {
 		t.Skip("skipping test in short mode.")
 	}
 
-	c, err := DialTimeout("[2001:660:3302:282a:204:75ff:fe9f:9e11]:21", 5*time.Second)
+	c, err := DialTimeout("[::1]:21", 5*time.Second)
 	if err != nil {
 		t.Fatal(err)
 	}