This pulls in and uses github.com/docker/docker/pkg/chrootarchive for the
actual copy up which is some battle hardened code to unpack avoiding things
like symlink traversal security issues.
However it does pull in a pretty huge pile of vendoring, including
github.com/docker/docker/pkg/reexec which we must then call at startup. It's
not immediately clear that this tradeoff is the correct one.
Signed-off-by: Ian Campbell <ijc@docker.com>
