Often the socket is put into the directory /run/containerd.
When this directory does not exist, it gets created with the
default uid/gid and permission 0660. When the user has specified
a uid or gid, this should be used to set the ownership of that
parent directory and the permissions should be 0770. This worked
in a previous version of containerd but regressed after a refactor.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>