Make sure err never gets masked

Defining err as named return parameter will make sure the variable gets
assigned before returning and thus avoid masking

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
fix docker integration-cli restart test race

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Replace old index image with hub

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)
Remove CheckSum from utils; replace with a TeeReader

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Partition server/ by image, init, events, container, and "everything left"

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Merge pull request #7331 from erikh/simplify_checksum

Simplify utils.CheckSum.Read to use TeeReader instead
Merge pull request #7317 from erikh/server_split

Partition server/ by image, init, events, container, and "everything left"
Make --attach case-insensitive

Docker-DCO-1.1-Signed-off-by: Tibor Vass <teabee89@gmail.com> (github: tiborvass)
Merge pull request #7298 from erikh/fix_cli_restart_test

fix docker integration-cli restart test race
Merge pull request #7100 from discordianfish/fix-port-allocation

Fix masked err in portmapper
Merge pull request #7325 from tiborvass/case-insensitive-attach

Make --attach case-insensitive
Fix graph/tags_unit_test.go on FreeBSD

- Directories should have u+x (0600 -> 0700)
- Don't chown files to root because we don't have to

Docker-DCO-1.1-Signed-off-by: Kato Kazuyoshi <kato.kazuyoshi@gmail.com> (github: kzys)
Remove perm change in archive
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #7340 from crosbymichael/tags-unit

Fix graph tags test on freebsd
Merge pull request #7328 from cpuguy83/fix_search_image_oldindex

Replace old index image with hub