title: broken pipe error returned in paramiko.ssh_exception.ProxyCommandFailure
body: <p>I am getting broken pipe error for the following code using paramiko</p>
  
  <pre><code> import paramiko
   proxy  = paramiko.ProxyCommand('/usr/bin/nc -vvv  -xhost:1080 %h %p')
   client = paramiko.SSHClient()
   client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
   client.connect('hostname', 22,username='user', password='pwd', sock=proxy)
   stdin, stdout, stderr = client.exec_command('ls')
   print "output", stdout.read()
   error = stderr.read()
   print "err", error, len(error)
   ftp = client.open_sftp() 
   ftp.get('file')
   ftp.close()
   client.close()
  </code></pre>
  
  <p>Error I am getting is 
  paramiko.ssh_exception.ProxyCommandFailure: ('/usr/bin/nc -vvv -w30 -xhost:1080 %h %p', 'Broken pipe')</p>