MXS-2219 Implement rudimentary Clustrix monitoring

The monitor now pings the health check ports of the Clustrix nodes.
A response translates to RUNNING and a non-response to DOWN.

server/modules/monitor/clustrixmon/clustrixmon.cc

@@ -41,6 +41,11 @@ extern "C" MXS_MODULE* MXS_CREATE_MODULE()
         NULL,                                       /* Thread init. */
         NULL,                                       /* Thread finish. */
         {
+            {
+                CLUSTER_MONITOR_INTERVAL_NAME,
+                MXS_MODULE_PARAM_COUNT,
+                DEFAULT_CLUSTER_MONITOR_INTERVAL_ZVALUE
+            },
             {MXS_END_MODULE_PARAMS}
         }
     };