Clean up the docker socket on termination of the daemon.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Add OS to docker info

Docker-DCO-1.1-Signed-off-by: Tibor Vass <teabee89@gmail.com> (github: tiborvass)
Merge pull request #7215 from tiborvass/add-os-to-docker-info

Add OS to docker info
Merge pull request #6962 from erikh/3349-cleanup-docker-socket

Clean up the docker socket on termination of the daemon.
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)