title: Pip installation stuck in infinite loop if unresolvable conflicts in dependencies
body: <p>Pip installation is stuck in an infinite loop if there are unresolvable conflicts in dependencies. To reproduce, <code>pip==20.3.0</code> and:</p>
  <pre><code>pip install pyarrow==2.0.0 azureml-defaults==1.18.0
  </code></pre>