FIX nginx use selected log formatting

installer/roles/image_build/files/nginx.conf

@@ -16,6 +16,8 @@ http {
                       '$status $body_bytes_sent "$http_referer" '
                       '"$http_user_agent" "$http_x_forwarded_for"';
 
+    access_log /dev/stdout main;
+
     map $http_upgrade $connection_upgrade {
         default upgrade;
         ''      close;