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/clustrixmonitor.hh

@@ -14,17 +14,52 @@
 
 #include "clustrixmon.hh"
 #include <maxscale/monitor.hh>
+#include <maxbase/http.hh>
 
 class ClustrixMonitor : public maxscale::MonitorInstance
 {
     ClustrixMonitor(const ClustrixMonitor&) = delete;
     ClustrixMonitor& operator=(const ClustrixMonitor&) = delete;
 public:
+    class Config
+    {
+    public:
+        Config()
+            : m_cluster_monitor_interval(DEFAULT_CLUSTER_MONITOR_INTERVAL_VALUE)
+        {
+        };
+
+        long cluster_monitor_interval() const
+        {
+            return m_cluster_monitor_interval;
+        }
+
+        void set_cluster_monitor_interval(long l)
+        {
+            m_cluster_monitor_interval = l;
+        }
+
+    private:
+        long m_cluster_monitor_interval;
+    };
 
     static ClustrixMonitor* create(MXS_MONITOR* pMonitor);
 
+    bool configure(const MXS_CONFIG_PARAMETER* pParams) override;
+
 private:
     ClustrixMonitor(MXS_MONITOR* pMonitor);
 
+    void pre_tick();
+
     void tick();
+
+    void initiate_delayed_http_check();
+    bool check_http(Call::action_t action);
+
+private:
+    Config                   m_config;
+    mxb::http::Async         m_http;
+    std::vector<std::string> m_health_urls;
+    uint32_t                 m_delayed_http_check_id;
 };