ES add_index management command should display errors

[bferguso]

When registering a custom index via the python manage.py es add_index --name command, if any errors are encountered creating the index, no error message is displayed and the creating index : {index name} message is displayed.

The es call is
self.es.options(ignore_status=400).indices.create(**kwargs), and the returned response is ignored.

The response should be captured and displayed if the command was not successful.