MXS-1845 Cluster stabilization rewrite

No longer writes events to the master, as this creates problems if the
promoted server was not the overall master. Instead, the slave status
output is inspected.

server/modules/monitor/mariadbmon/mariadbserver.hh

@@ -281,6 +281,15 @@ public:
      */
     const SlaveStatus* slave_connection_status(const MariaDBServer* target) const;
 
+    /**
+     * Find slave connection to the target server. Only considers host and port when selecting
+     * the connection. A matching connection is accepted even if its IO or SQL thread is stopped.
+     *
+     * @param target Immediate master or relay server
+     * @return The slave status info of the slave thread, or NULL if not found
+     */
+    const SlaveStatus* slave_connection_status_host_port(const MariaDBServer* target) const;
+
     /**
      * Is binary log on? 'update_replication_settings' should be ran before this function to query the data.
      *