第二部分
创建管理资源池
可扩展预留介绍
expandable reservation allows a resource pool to "borrow" resources from its parent host or parent resource pool in order to satisfy reservations set on individual virtual machnines within the resource pool.note that a resource pool with an expandable reservation would only "borrow" from the parent in order to satisfy reservations,not in order to satisfy requests for resources in excess of the reservations(如果预留资源不够,无法开机,可以像父资源池借用资源来预留资源)
