Allow monitors and services to start without servers

MaxScale can now start without any defined monitors. This allows the core
services to be configured beforehand. With the changes to dynamic
modifications to servers, automatic scaling of slaves is possible.

server/core/service.c

@@ -821,13 +821,12 @@ void serviceRemoveBackend(SERVICE *service, const SERVER *server)
 {
     spinlock_acquire(&service->spin);
 
-    service->n_dbref--;
-
     for (SERVER_REF *ref = service->dbref; ref; ref = ref->next)
     {
         if (ref->server == server)
         {
             ref->active = false;
+            service->n_dbref--;
             break;
         }
     }