Use ondemand instead of dynamic

I believe ondemand is much more efficient on resource usage.

install/ubuntu/16.04/php-fpm/www.conf

@@ -1,10 +1,11 @@
 [www]
 listen = 127.0.0.1:9000
 listen.allowed_clients = 127.0.0.1
+
 user = www-data
 group = www-data
-pm = dynamic
-pm.max_children = 50
-pm.start_servers = 5
-pm.min_spare_servers = 3
-pm.max_spare_servers = 35
+
+pm = ondemand
+pm.max_children = 2
+pm.max_requests = 4000
+pm.process_idle_timeout = 10s