title: pip install failing with 407 Proxy Authentication Required
body: <p>I am trying to use the below pip install command, but its failing with Proxy authentication required issue. I have already configured my proxies inside my RHEL7.x Server.</p>
  
  <pre><code>Command Used: `pip install --proxy https://'username:pwd'@proxy:host  --upgrade pip`
  </code></pre>
  
  <p>Logs:</p>
  
  <pre><code>Retrying (Retry(total=4, connect=None, read=None, redirect=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', error('Tunnel connection failed: 407 Proxy Authentication Required',))': /simple/pip/
  Retrying (Retry(total=3, connect=None, read=None, redirect=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', error('Tunnel connection failed: 407 Proxy Authentication Required',))': /simple/pip/
  Retrying (Retry(total=2, connect=None, read=None, redirect=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', error('Tunnel connection failed: 407 Proxy Authentication Required',))': /simple/pip/
  Retrying (Retry(total=1, connect=None, read=None, redirect=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', error('Tunnel connection failed: 407 Proxy Authentication Required',))': /simple/pip/
  Retrying (Retry(total=0, connect=None, read=None, redirect=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', error('Tunnel connection failed: 407 Proxy Authentication Required',))': /simple/pip/
  </code></pre>