下载最新的CENTOS8，最小安装包500M左右，不用下载全包
https://mirrors.aliyun.com/centos/8.0.1905/isos/x86_64/安装的时候设置基础仓库源：
https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/https://mirrors.aliyun.com/centos/8.0.1905/isos/x86_64/https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/