MXS-1929: Always store the module name parameter

Services, monitors and filters all use the parameters for object
serialization. This means that when the object is created, the module
parameter must be in the parameter list.

server/core/monitor.cc

@@ -155,6 +155,9 @@ MXS_MONITOR* monitor_create(const char *name, const char *module, MXS_CONFIG_PAR
     monitor_add_user(mon, config_get_string(params, CN_USER),
                      config_get_string(params, CN_PASSWORD));
 
+    // Store module, used when the monitor is serialized
+    monitor_set_parameter(mon, CN_MODULE, module);
+
     monitor_add_parameters(mon, params);
 
     if ((mon->instance = mon->api->createInstance(mon)) == NULL)