title: Let's Encrypt certbot-auto fails because a Python / pip problem
body: <p>Yesterday all was fine, but today, running the same command using certbot-auto to renew a certificate, I get this :</p>
  
  <pre><code>Upgrading certbot-auto 0.31.0 to 0.32.0...
  Replacing certbot-auto...
  Creating virtual environment...
  Installing Python packages...    
  /opt/eff.org/certbot/venv/bin/python: No module named pip.__main__; 'pip' is a package and cannot be directly executed
      Traceback (most recent call last):
        File "/tmp/tmp.eUWQ3w7cFV/pipstrap.py", line 177, in &lt;module&gt;
          sys.exit(main())
        File "/tmp/tmp.eUWQ3w7cFV/pipstrap.py", line 149, in main
          pip_version = StrictVersion(check_output([python, '-m', 'pip', '--version'])
        File "/usr/lib/python2.7/subprocess.py", line 544, in check_output
          raise CalledProcessError(retcode, cmd, output=output)
      subprocess.CalledProcessError: Command '['/opt/eff.org/certbot/venv/bin/python', '-m', 'pip', '--version']' returned non-zero exit status 1
  </code></pre>
  
  <p>I'm on Debian 7.9... someone with the same problem ?</p>