Calling close_write on io if necessary

[tlunter]

Finishes #240 by fixing the ABC complexity error

@bfulton @nahiluhmot @jschneiderhan @myers

This seemed to work appropriately when I tried it locally. I would expect the small script I wrote (attached) to hang since the write end would never be closed, but it ends and prints the output from cat.

require 'docker'

Docker.options[:ssl_verify_peer] = false

image = Docker::Image.create('fromImage' => 'ubuntu:14.04')

container = Docker::Container.create('Image' => 'ubuntu', 'Cmd' => ['cat'], 'OpenStdin' => true, 'StdinOnce' => true)
puts container.tap(&:start).attach(stdin: StringIO.new("foo\nbar\n"))

[bfulton]

+1