MXS-1775 Introduce MonitorInstance::configure() function

The configuring of the monitor instance is now performed in a
separate function. That is in preparation for the moving of the
start function to maxscale::MonitorInstance.

server/modules/monitor/mmmon/mmmon.hh

@@ -42,5 +42,7 @@ private:
 
     MXS_MONITORED_SERVER *get_current_master();
 
+    void configure(const MXS_CONFIG_PARAMETER* params);
+
     void main();
 };