title: python ssh without authenticity validation
body: <p>I am running a command remotely on an AWS machine like this:</p>
  
  <pre><code>key = 'myPemFile.pem'
  target = &lt;machine_ip&gt;
  cmd = 'ssh -i ' + key + ' ubuntu@'+target+' "nohup myprog + ' &gt;&amp; /dev/null &lt; /dev/null &amp;" &amp;'
  proc = subprocess.Popen(cmd, shell=True,  stdout=subprocess.PIPE)
  </code></pre>
  
  <p>This works fine, but if it is the first login onto the machine I get the question:</p>
  
  <pre><code>The authenticity of host '144.224.18.97 (144.224.18.97)' can't be established.
  ECDSA key fingerprint is e2:4e:...:e3:73:07.
  Are you sure you want to continue connecting (yes/no)
  </code></pre>
  
  <p>how do I "input" "yes" from python, or alternatively, use a flag to tell ssh not to ask the question?</p>