MXS-1775 Handle connection error the same way

All monitors (but for MariaDBMon) now handle connection errors in
the same manner.

An exception is MMMon that modifies both the server status and the
monitor status. However, in fact, all other monitors do it the wrong
way and update the server status directly instead of only the monitor
status that then at the end of the loop should be copied to the server
status.

server/modules/monitor/ndbclustermon/ndbclustermon.cc

@@ -139,6 +139,10 @@ void NDBCMonitor::update_server_status(MXS_MONITORED_SERVER* monitored_server)
         {
             server_set_status_nolock(monitored_server->server, SERVER_AUTH_ERROR);
         }
+        else
+        {
+            server_clear_status_nolock(monitored_server->server, SERVER_AUTH_ERROR);
+        }
 
         monitored_server->server->node_id = -1;