Runs event hooks for registered event plugins.

            `shutdown`
                Set to ``True`` to run task_end events;
                otherwise, run task_run events.

def _run_events(self, shutdown=False):
        """ Runs event hooks for registered event plugins.

            `shutdown`
                Set to ``True`` to run task_end events;
                otherwise, run task_run events.
            """

        # run task_start events, if not ran already
        if not self._ran_taskstart:
            self._ran_taskstart = True
            registration.run_event_hooks('task_start', self._task)

        # run events
        event = 'task_end' if shutdown else 'task_run'
        registration.run_event_hooks(event, self._task)

        # reclaim any subprocesses plugins may have forked
        try:
            os.waitpid(-1, os.P_NOWAIT)
        except OSError:
            pass