Improve test coverage for `fetch_recursive`

[darrenklein]

While investigating something else, I noticed that none of our test cases ever end up recursively calling the Query module's fetch_recursive private method - it would probably be a good idea to write a test to cover that scenario.

[darrenklein]

The test would need to make sure fetch_result["LastEvaluatedKey"] != nil and updated_recursive.continue evaluated to true.