MXS-2314 Server added to monitor should be added to service

If the servers of a service are defined by a monitor (the config
has 'cluster=SomeMonitor'), then the addition of a server to a
a monitor should lead to that server being added to the service.

server/core/service.cc

@@ -161,6 +161,19 @@ void service_add_server(Monitor* pMonitor, SERVER* pServer)
     }
 }
 
+void service_remove_server(Monitor* pMonitor, SERVER* pServer)
+{
+    LockGuard guard(this_unit.lock);
+
+    for (Service* pService : this_unit.services)
+    {
+        if (pService->m_monitor == pMonitor)
+        {
+            serviceRemoveBackend(pService, pServer);
+        }
+    }
+}
+
 Service::Service(const std::string& service_name,
                  const std::string& router_name,
                  MXS_CONFIG_PARAMETER* params)