fix "/" can't be the tar target

Docker-DCO-1.1-Signed-off-by: cheneydeng <cheneydeng@qq.com> (github: )
Merge branch 'cheneydeng_dev' of github.com:cheneydeng/docker into cheneydeng_dev

Docker-DCO-1.1-Signed-off-by: cheneydeng <cheneydeng@qq.com> (github: )