title: Cannot run multiple kernels (Python versions) in jupyterhub
body: <p>Hi I am running a notebook server with jupyterhub but I am unable to access different kernels (version of python).</p>
  
  <p>I have the various enronments setup correctly, and when I type </p>
  
  <pre><code>jupyter kernelspec list
  </code></pre>
  
  <p>I get the following output</p>
  
  <pre><code>Available kernels:              
  bash       /home/username/.local/share/jupyter/kernels/bash  
  python2    /usr/local/share/jupyter/kernels/python2                  
  python3    /usr/local/share/jupyter/kernels/python3
  </code></pre>
  
  <p>But when the jupyterhub launches it only finds the Python3 kernel available?</p>
  
  <p>How can I get it to detect all available python versions??</p>
  
  <pre><code>cat /usr/local/share/jupyter/kernels/python2/kernel.json  
  
  {                                                   
  "display_name": "Python 2",
  "language": "python",
  "argv": [
  "/opt/anaconda3/envs/py27/bin/python2.7",
  "-m",
  "ipykernel",
  "-f",
  "{connection_file}"                                                        
  ]       
  }
  
  cat /usr/local/share/jupyter/kernels/python3/kernel.json  
  
  { 
  "language": "python",                                                 
  "display_name": "Python 3",
  "argv": [
  "/opt/anaconda3/bin/python3",
  "-m",
  "ipykernel",
  "-f",
  "{connection_file}"                                                        
  ] 
  }
  </code></pre>