Returns the number of cores reserved in this moment.
        A core is reserved if it's still not running but
        we have submitted the task to the queue manager.

def ncores_reserved(self):
        """
        Returns the number of cores reserved in this moment.
        A core is reserved if it's still not running but
        we have submitted the task to the queue manager.
        """
        return sum(task.manager.num_cores for task in self if task.status == task.S_SUB)