title: gsutil parallel deletion on empty buckets
body: <p>We're getting errors when trying to run <code>gsutil -m rm -r gs://bucketname</code> if the bucket itself is empty:</p>
  
  <pre><code>$ gsutil -m rm -r gs://scoletestbucket
  Removing gs://scoletestbucket/...
  CommandException: 1 files/objects could not be removed.
  $ echo $?
  1
  </code></pre>
  
  <p>Despite the error message, though, the command does exactly what we want it to do: it removes the bucket. But our scripting that's monitoring command return codes naturally thinks the gsutil command is reporting an error.</p>
  
  <p>Everything works as expected if we leave off the parallelism option (<code>-m</code>), but we'd kind of like to keep it if possible, for the situations when we're actually deleting bunches of stuff.</p>
  
  <p>Are we missing something, or is this a bug?</p>