MXS-2169 Allow a downed server to be selected as topology master

This is required for the case when MaxScale is started when the master is
already down.

server/modules/monitor/mariadbmon/mariadbserver.cc

@@ -52,7 +52,6 @@ NodeData::NodeData()
 void NodeData::reset_results()
 {
     cycle = CYCLE_NONE;
-    reach = REACH_UNKNOWN;
     parents.clear();
     children.clear();
     external_masters.clear();