RedHat 启动 docker报错：
错误：Error starting daemon: SELinux is not supported with the overlay2 graph driver on t...=false)
解决方法：
https://stackoverflow.com/questions/45461307/selinux-is-not-supported-with-the-overlay-graph-driver
RedHat7安装docker的方法：
https://stackoverflow.com/questions/45461307/selinux-is-not-supported-with-the-overlay-graph-driver