Log Message:
Update databases/py-elasticsearch to 2.4.0.

2.4.0 (2016-08-17)
- ping now ignores all TransportError exceptions and just returns
  False
- expose scroll_id on ScanError
- increase default size for scan helper to 1000
- changed Transport.perform_request to just return the body, not
  status as well.

2.3.0 (2016-02-29)
- added client_key argument to configure client certificates
- debug logging now includes response body even for failed requests