title: Unable to download/upload App Engine data due to 'Illegal string "dev~None" in dataset id.'
body: <p>I receive the following error:</p>
  
  <pre><code>google.appengine.api.datastore_errors.BadRequestError: \
      Illegal string "dev~None" in dataset id.
  </code></pre>
  
  <p>When I try to use my production database in my local development environment:</p>
  
  <pre><code>$ appcfg.py download_data \
      --application=s~app-id \
      --url=http://app-id.appspot.com/_ah/remote_api \
      --filename=database.ndb
  
  $ appcfg.py upload_data \
      --application=dev~app-id \
      --url=http://localhost:53828/_ah/remote_api \
      --filename=database.ndb
  </code></pre>
  
  <p>Any tips?  My best guess is that something is broken by the transition from <code>appcfg.py</code> to <code>gcloud</code>. I use the latter most of the time, but I can't find a way to accomplish this task using <code>gcloud</code>. Thanks!</p>