Add "docker create" support

This PR is for the remaining two commits for docker create. (https://github.com/dotcloud/docker/pull/4548)

This exposes the already existing "create container" operation. It is
very similar to "docker run -d" except it doesn't actually start the
container, but just prepares it. It can then be manually started using
"docker start" at any point.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson alexl@redhat.com (github: alexlarsson)