Move execute_worker_task into mxs::Worker

The function has use outside of the monitors as it makes execution of
worker tasks much more convenient. Currently, this change only moves the
code and takes it into use: there should be no functional changes.

include/maxscale/monitor.hh

@@ -22,7 +22,7 @@ namespace maxscale
 {
 
 class MonitorInstance : public  MXS_MONITOR_INSTANCE
-                      , private maxscale::Worker
+                      , protected maxscale::Worker
 {
 public:
     MonitorInstance(const MonitorInstance&) = delete;
@@ -112,8 +112,6 @@ public:
     virtual json_t* diagnostics_json() const;
 
 protected:
-    typedef std::function<void ()> GenericFunction;
-
     MonitorInstance(MXS_MONITOR* pMonitor);
 
     const std::string& script() const { return m_script; }
@@ -210,16 +208,6 @@ protected:
      */
     virtual void process_state_changes();
 
-    /**
-     * Execute a task in the worker thread of this monitor.
-     *
-     * @param func The task which should be executed, wrapped in a function object.
-     * @param mode Execution mode. If EXECUTE_AUTO, the function will only return once the task has
-     * been executed. Otherwise, the task will be queued and the function returns immediately.
-     * @return True, if task was sent to the worker
-     */
-    bool execute_worker_task(GenericFunction func, execute_mode_t mode = Worker::EXECUTE_AUTO);
-
     MXS_MONITOR*          m_monitor;  /**< The generic monitor structure. */
     MXS_MONITORED_SERVER* m_master;   /**< Master server */