If attaching to stdin, set StdinOnce, as per the docker CLI.
Support requests >=2.1.0

Starting with requests 2.1.0 non-HTTP scheme URLs are not parsed anymore.
The net effect of this is that when using the unix socket in docker-py no
query string params are passed in the URL.  This change makes docker-py
internally use the scheme http+unix to indicate to requests that this is
still a HTTP URL and should be parsed.

Users of docker-py can still specify 'unix:' as the base_url.  The
following forms of base_url are accepted.

  http+unix://var/run/docker.sock
  unix://var/run/docker.sock
  unix:///var/run/docker.sock
  http://hostname
  tcp://hostname
flake8 fixes

Additionally this change should make moving to /v1.8 slightly less painful
Allow links to specified as (name, alias) tuples
Update to requests==2.2.1
Merge pull request #153 from bfirsh/links-as-tuples

Allow links to specified as (name, alias) tuples
Merge pull request #145 from aanand/set-stdinonce

If attaching to stdin, set StdinOnce, as per the docker CLI.
Merge pull request #151 from ibuildthecloud/http-unix-scheme

Support requests >=2.1.0
Fix unit tests broken by PR #151

Updates newer unit tests to use the http+unix scheme.
Merge pull request #154 from ibuildthecloud/fix-post-http-unix-merge-tests

Fix unit tests broken by PR #151