docker daemon: show info about the server

For combing through logs, have an intro line with information about the
running instance of the docker daemon.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #4990 from vbatts/vbatts-server_show_info

docker daemon: show info about the server