previous document suggests to put config to /root/.docker/config.json
which is not always the case, and only works when the HOME=/root is
set for kubelet. Besides, that's not always the most recommended way
considering the potential risk when someone overrides this config
with another `docker login` on the same node. this change explicitly
lists all the possible locations where the configuration can be put.
zhouhaibing089
ce190e75f8