MXS-502: Server state changes are logged at notify level

When MaxScale perceives a state change in one of the servers it will log
an message into the log file stating the previous and the current state.
This will make it easier to analyze failures in the cluster.

server/modules/monitor/mmmon.c

@@ -652,7 +652,7 @@ monitorMain(void *arg)
                 evtype = mon_get_event_type(ptr);
                 if (isMySQLEvent(evtype))
                 {
-                    MXS_INFO("Server changed state: %s[%s:%u]: %s",
+                    MXS_NOTICE("Server changed state: %s[%s:%u]: %s",
                              ptr->server->unique_name,
                              ptr->server->name, ptr->server->port,
                              mon_get_event_name(ptr));