Add tests for ConfigurationManager.extract_payload

- test_missing_operation

  A Payload without a "operation" key raises a MessageFormatError.

- test_missing_target

  A Payload without a "target" key raises a MessageFormatError.

- test_missing_collection

  A Payload without a "collection" key raises a MessageFormatError.

- test_return_value

  'ConfigurationManager.extract_payload returns a tuple with the
  elements (operation, target, collection).