title: Not able to automate CTS running on multiple devices using Python
body: <p>I am trying to automate CTS automatically with Python. I can use that on single device but can't run on multiple devices with same python code(subprocess.Popen) .</p>
  <p>['android-cts/tools/cts-tradefed', 'run', 'cts', '--shards', '1'] works</p>
  <p>['android-cts/tools/cts-tradefed', 'run', 'cts', '--shards', '2']doesn't work</p>
  <p>My question is how can I start shards CTS testing with python to automatically test CTS on multiple devices?</p>