Fix Issue 44 - Get the docker client from the tgz file

[aranaea]

This fixes issue #44. On my system I was not getting a valid docker executable. I couldn't find a way to directly download the docker client, even using the url constructed in the code. I could find a tgz file, though. This change pulls the tgz file for your version and copies out the docker client.

Tested with Docker 1.11.2

[gdevillele]

Thanks for contributing.
Could would please run go fmt ./go/src/gosetup/main.go please?
So that the file you edited is formatted correctly.

Except this, it LGTM.
(We must find a reliable mirror to download docker binaries from, though)

[gdevillele]

Ok,
we must use the .tgz suffix for docker 1.11 and up but keep the previous way of getting docker binaries for version 1.10.x and older. @aranaea, could you update your PR to do that, so it doesn't break for 1.10 version and older? Thanks.

[aranaea]

Sure thing. I should have an update in a couple days.

[aranaea]

@gdevillele These latest commits are working for me but I can't easily test with versions older than 1.11.0. If you find that it's broken for older versions I can set something up so that I can address the problems.

Also, this is really the first go that I've written so please let me know if it looks weird.

[gdevillele]

LGTM. Thank you.