fix log format for nginx cache stats in munin, fixes #20546

2.Common_services/5.Nginx/vhost_cache.conf

 proxy_cache_path /tmp/nginx-uc-cache levels=1:2 keys_zone=uc-cache:10m max_size=10g inactive=300s;
 
+log_format cache '$remote_addr - $host [$time_local] "$request" $status '
+    '$body_bytes_sent "$http_referer" '
+    'rt=$request_time ut="$upstream_response_time" '
+    'cs=$upstream_cache_status';
+
 server {
     listen 80 default_server;
     listen 443 default_server ssl;
@@ -7,7 +12,7 @@ server {
 
     root /var/www/cache/;
 
-    access_log /var/log/nginx/access_cache.log;
+    access_log /var/log/nginx/access_cache.log cache;
     error_log /var/log/nginx/error_cache.log;
 
     location /crossdomain {