查看虚拟机设置中关于CDROM的选项，将CD-ROM改到最上边，就好了
修改的方法：http://jingyan.baidu.com/article/9faa723183eea7473d28cb6f.html
虚拟机：The centos disc was not found in any of your drives. Please insert the centos disc and press OK to retry
原文：http://www.cnblogs.com/mswangblog/p/6618945.html
