roles/nginx: Fix munin.conf for nginx_status

This config stopped working a few years ago probably when hosts started
getting IPv6 and we need to allow ::1. Make sure we're only listening
on local loopback interfaces also.

roles/nginx/files/munin.conf

@@ -1,6 +1,8 @@
 # nginx status module + munin aliases
 server {
-    listen localhost:80;
+    listen 127.0.0.1:80;
+    listen [::]:80;
+    server_name localhost;
 
     log_not_found off;
 
@@ -8,6 +10,7 @@ server {
         stub_status on;
         access_log off;
         allow 127.0.0.1;
+        allow ::1;
         deny all;
     }
 
@@ -18,7 +21,6 @@ server {
 
     location /munin/ {
         alias /var/cache/munin/www/;
-        index index.html
         expires modified +310s;
     }
 }