docker build -t xiaopeng163/centos-entrypoint-shell .
有了image 以後，就可以創建container
執行 docker run xiaopeng163/centos-entrypoint-shell 創建一個容器
打印出 hello Docker
docker run xiaopeng163/centod-entrypoint-exec
打印出 hello $name
vim Dockerfile 
docker build -t xiaopeng163/centos-entrypoint-exec-new .
docker run xiaopeng163/centod-entrypoint-exec-new
打印出 hello Docker