title: Access denied while loading from gcs to bigquery
body: <p>I have uploaded a csv file to gcs and I can list/view that file using "gsutil(ls and cat)". I can even load that file using "bq load" but when I try to load it from the python loadTable script mentioned in the examples, it fails with the error message "Access Denied"</p>
  
  <pre><code>{u'state': u'DONE', u'errors': [{u'reason': u'accessDenied', u'message': u'Access Denied: File (file_name): Access Denied'}], u'errorResult': {u'reason': u'accessDenied', u'message': u'Access Denied: File (file_name): Access Denied'}}
  </code></pre>
  
  <p>Done Loading!</p>
  
  <p>The authorization used is through "Service account" key. I have tested the listing of dataset and the table. Its just the upload through gcs which says "Access Denied".</p>
  
  <p>Please help.</p>