Add monitor reconfiguration helper

The MonitorManager function reconfigured a monitor and rolls back to the
old configuration if the new one doesn't work.

server/core/internal/monitor.hh

@@ -149,6 +149,18 @@ public:
      */
     static bool monitor_serialize(const mxs::Monitor* monitor);
 
+    /**
+     * Attempt to reconfigure a monitor
+     *
+     * If the configuration fails, the old parameters are restored.
+     *
+     * @param monitor    Monitor to reconfigure
+     * @param parameters New parameters to apply
+     *
+     * @return True if reconfiguration was successful
+     */
+    static bool reconfigure_monitor(mxs::Monitor* monitor, const MXS_CONFIG_PARAMETER& parameters);
+
     /**
      * @brief Convert monitor to JSON
      *