Add Sockets (-H) list to `docker -D info`.

This will allow us to _know_ what the user's -H settings are, which may
be useful for debugging later.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
move api docs to APIv1.13

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #5413 from SvenDowideit/docker-info-list-sockets

Add Sockets (-H) list to `docker -D info`.