Add tests for ConfigurationManager.handle_request

test_reply_error_request_value_database_error

  'reply_error' is called with the correct arguments when a
  DatabaseError occurs in handle_request_value

test_reply_error_write_value_message_error

  'reply_error' is called with the correct arguments when a
  MessageFormatError occurs in handle_write_value

test_reply_error_write_value_database_error

  'reply_error' is called with the correct arguments when a
  MessageFormatError occurs in handle_write_value
Handle InvalidId in MessageEncoderMongoDB.hook
Fix MessageEncoderMongoDB.replace_id

The "object_id" and "_id" keys were mixed-up.
Add `Cursor' handling in MessageEncoderMongoDB.default