Docker should use /var/lib/docker/tmp for large temporary files.

/tmp is often a tmpfs file system and large temporary files could cause
docker commands to fail.

Fixes #4396

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Any particular reason we're ignoring any errors from `MkdirAll`?  Would it be prudent to either not do that, or add a comment as to why we're doing that?