title: ImportError: No module named ssl_match_hostname when importing the docker SDK for Python
body: <p>In order to use the <a href="https://docker-py.readthedocs.io/en/stable/client.html" rel="noreferrer">Docker SDK for Python</a>, I'm trying to <code>import docker</code> in a Python script, but it's resulting in an <code>ImportError</code> with the following traceback:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/home/kurt/dev/clones8/ipercron-compose/furion/iclib/tests/test_utils/docker_utils.py", line 1, in &lt;module&gt;
      import docker
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/__init__.py", line 6, in &lt;module&gt;
      from .client import Client, AutoVersionClient, from_env # flake8: noqa
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/client.py", line 11, in &lt;module&gt;
      from . import api
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/api/__init__.py", line 2, in &lt;module&gt;
      from .build import BuildApiMixin
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/api/build.py", line 9, in &lt;module&gt;
      from .. import utils
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/utils/__init__.py", line 2, in &lt;module&gt;
      from .utils import (
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/utils/utils.py", line 19, in &lt;module&gt;
      from .. import tls
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/tls.py", line 5, in &lt;module&gt;
      from .ssladapter import ssladapter
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/ssladapter/__init__.py", line 1, in &lt;module&gt;
      from .ssladapter import SSLAdapter # flake8: noqa
    File "/home/kurt/.local/lib/python2.7/site-packages/docker/ssladapter/ssladapter.py", line 21, in &lt;module&gt;
      from backports.ssl_match_hostname import match_hostname
  ImportError: No module named ssl_match_hostname
  [Finished in 0.2s with exit code 1]
  [shell_cmd: python -u "/home/kurt/dev/clones8/ipercron-compose/furion/iclib/tests/test_utils/docker_utils.py"]
  [dir: /home/kurt/dev/clones8/ipercron-compose/furion/iclib/tests/test_utils]
  [path: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin]
  </code></pre>
  
  <p>The strange thing is that the import does work in other places, for example in an iPython prompt:</p>
  
  <pre><code>Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
  Type "copyright", "credits" or "license" for more information.
  
  IPython 2.4.1 -- An enhanced Interactive Python.
  ?         -&gt; Introduction and overview of IPython's features.
  %quickref -&gt; Quick reference.
  help      -&gt; Python's own help system.
  object?   -&gt; Details about 'object', use 'object??' for extra details.
  
  In [1]: import docker
  
  In [2]: 
  </code></pre>
  
  <p>Why is the import not working in the first case?</p>