docker overlay2 空间占满100%时，处理方法

引用自：https://unix.stackexchange.com/questions/414483/docker-increase-available-disk-space
跟换overlay2目录地址：
You could move the docker directory to somewhere under /home and create a symlink /var/lib/docker pointing to the new location. For example:

shut down docker first

mv /var/lib/docker /home/
ln -s /home/docker/ /var/lib/

restart docker now

Use another directory if /home/docker already exists.

Instead of, or as well as, the symlink from /var/lib/docker -> /home/docker, you could also reconfigure docker so that it expects to find its directory under /home rather than /var/lib.