Support docker-ce

[scoopex]

It seems that the structure of the docker apt repositories changed again :-(

The module should support the installation procedure described at:
https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/#install-docker-ce-1

I you want like to install docker-ce on artful, you should use the zesty source, because the artful source does not contain packages:

# w3m -dump https://download.docker.com/linux/ubuntu/dists/zesty/pool/stable/amd64/
Index of /linux/ubuntu/dists/zesty/pool/stable/amd64/

-------------------------------------------------------------------------------

../
docker-ce_17.06.0~ce-0~ubuntu_amd64.deb  2017-06-28 05:17  20M
docker-ce_17.06.1~ce-0~ubuntu_amd64.deb  2017-08-18 02:35  20M
docker-ce_17.06.2~ce-0~ubuntu_amd64.deb  2017-09-05 10:39  20M
docker-ce_17.09.0~ce-0~ubuntu_amd64.deb  2017-09-27 01:48  21M

-------------------------------------------------------------------------------
# w3m -dump https://download.docker.com/linux/ubuntu/dists/artful/pool/stable/amd64/
Index of /linux/ubuntu/dists/artful/pool/stable/amd64/

-------------------------------------------------------------------------------

../

-------------------------------------------------------------------------------

# grep docker /etc/apt/sources.list
deb [arch=amd64] https://download.docker.com/linux/ubuntu zesty stable
# deb-src [arch=amd64] https://download.docker.com/linux/ubuntu artful stable

What a mess.....

I filed a bug at the docker bugtracker: docker/docs#5284