resume pulling the layer on disconnect

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
pull only busybox:latest

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
fix busybox image detection

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #6165 from vieux/update_tests

Update tests regarding busybox & inspect
switch skipping from error to debug

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #6166 from vieux/debug_skipping

switch skipping from error to debug
Merge pull request #5848 from unclejack/resumable_pulls

resume pulling the layer on disconnect
Ensure that ownership and perms are copied to volume

This only works if the file or dir is already created in
the image before setting it to be a volume.  There is no way around this
because we don't have the data avaliable to set the volume at the
beginning of the dockerfile
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Add test for volume ownership and perms
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)