MXS-2314 Populate services with servers

The services whose servers are defined using a monitor, will
now be populated from the monitor.

Note, no consideration has yet been given to runtime changes.

server/modules/monitor/clustrixmon/clustrixmonitor.hh

@@ -64,6 +64,8 @@ public:
 
     bool configure(const MXS_CONFIG_PARAMETER* pParams) override;
 
+    void populate_services() override;
+
     bool softfail(SERVER* pServer, json_t** ppError);
     bool unsoftfail(SERVER* pServer, json_t** ppError);