This corrects `docker cp` behavior when user namespaces are enabled.
Instead of chown'ing copied-in files to real root (0,0), the code
queries for the remapped root uid & gid and sets the chown option
properly.
Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
