MXS-1775 Monitor loop and monitoring separated

In preparation for moving the monitor loop to MonitorInstance.

server/modules/monitor/grmon/grmon.hh

@@ -39,6 +39,7 @@ private:
 
     bool has_sufficient_permissions() const;
     void configure(const MXS_CONFIG_PARAMETER* params);
+    void tick();
 
     void main();
 };