Created by: qingqing01

Even though we can use int type to express bool type. But if use int type, some checking code in operators is as follow:

    PADDLE_ENFORCE(ctx.Attr<int>("is_training") == 0 ||
                   ctx.Attr<int>("is_training") == 1);

And the bool type attributes are used frequently in operators. So, I think it's necessary to add bool type.