title: Use already existing VM with TPU
body: <p>According to <a href="https://github.com/tensorflow/tpu/tree/master/tools/ctpu" rel="nofollow noreferrer">ctpu documentation</a> I can use following commands: <code>status</code>, <code>up</code>, <code>pause</code> and <code>delete</code>, where <code>up</code> does the following " ctpu up will create a Compute Engine VM with TensorFlow pre-installed".<br>
  However, I already have a VM on GCP I am working with. All my machine learning scripts are there. I even executed them successfully but they execute slow and I want to use preemptible TPU.
  How can I connect my VM to use TPU instead of creating new VM?</p>