title: Elasticsearch delete_by_query wrong usage
body: <p>
  I am using 2 similar ES methods to load and delete documents:</p>
  
  <pre><code>result = es.search(index='users_favourite_documents',
                     doc_type='favourite_document',
                     body={"query": {"match": {'user': user}}})
  </code></pre>
  
  <p>And:</p>
  
  <pre><code>result = es.delete_by_query(index='users_favourite_documents',
                              doc_type='favourite_document',
                              body={"query": {"match": {'user': user}}})
  </code></pre>
  
  <p>First one works ok and returns expected records.<br>
  Second one throws Exception:</p>
  
  <blockquote>
    <p>"TransportError(404,'{<br>
    \"found\":false,<br>
    \"_index\":\"users_favourite_documents\",<br>
    \"_type\":\"favourite_document\",<br>
    \"_id\":\"_query\",
    \"_version\":1,<br>
    \"_shards\":{\"total\":2,\"successful\":2,
    \"failed\":0}}')"</p>
  </blockquote>
  
  <p>What am I doing wrong?</p>