title: paramiko SSHClient connect stuck
body: <p>i have 3 source code(main and imported from it).</p>
  
  <h2>test.py - just import file</h2>
  
  <pre><code>import test_child
  </code></pre>
  
  <h2>test_child.py - call function defined in imported file</h2>
  
  <pre><code>import test_grandchild
  
  test_grandchild.check_sshd()
  </code></pre>
  
  <h2>test_grandchild.py - define function</h2>
  
  <pre><code>import paramiko
  
  def check_sshd():
      client = paramiko.SSHClient()
      client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
      print('checking ssh connection to local host')
      client.connect('127.0.0.1')
      client.close()
      print('finished')
  </code></pre>
  
  <p>check_ssd() is a fucntion just for checking sshd is running on localhost, So it is my expecting that Authentication execption occur when sshd is not running, otherwise socket error.
  When i run test_child.py, result is in my expecting. but paramiko client get stucked on connect() and I have to terminate the process.</p>
  
  <pre><code>$ python test.py                                                                        
  checking ssh connection to local host
  ^CTraceback (most recent call last):
    File "test.py", line 4, in &lt;module&gt;
      import test_child
    File "/root/tests/test_child.py", line 6, in &lt;module&gt;
      test_grandchild.check_sshd()
    File "/root/tests/test_grandchild.py", line 10, in check_sshd
      client.connect('127.0.0.1')
    File "build/bdist.linux-x86_64/egg/paramiko/client.py", line 242, in connect
    File "build/bdist.linux-x86_64/egg/paramiko/transport.py", line 342, in start_client
    File "/usr/lib64/python2.7/threading.py", line 621, in wait
      self.__cond.wait(timeout, balancing)
    File "/usr/lib64/python2.7/threading.py", line 361, in wait
      _sleep(delay)
  KeyboardInterrupt
  </code></pre>
  
  <p>how can i solve this problem?</p>
  
  <p>Paramiko 1.12.4 on CentOS 7</p>
  
  <p>Thanks.</p>