title: paramiko hangs at _get_channel while using multiprocessing
body: <p>I have the following code (written using paramiko) which gets called in multiprocessing process</p>
  
  <pre><code>       def traffic(q, e):
              e.open()
  
         def open()
              assert self.closed
              self._channel = self._get_channel()
              self.stdin      = io.TextIOWrapper(CommandStdIn(self._channel))
              self.stdout = self._channel.makefile()
              self.stderr = self._channel.makefile_stderr()
  
         q = Queue()
         p = Process(target = self.traffic, args = (q, other_args))
         p.start()
         p.join()
  </code></pre>
  
  <p>Without multiprocessing, this works just fine. But with multiprocessing, it stops at</p>
  
  <pre><code> %paramiko.transport-WARNING: Success for unrequested channel! [??]
   %paramiko.transport-ERROR: Channel request for unknown channel 19
  </code></pre>
  
  <p>It hangs at the <code>self._get__channel()</code> part. What could be the reason?</p>