When Using subtest, all subtest captured output is written into the Parent Output Property

[BethanyG]

If a user has used print() or other debugging methods in their code and the tests for that code are using unittest.subtest, the captured output for the subtests is being written into the parent output property in the results.json file -- one set of of output for each subtest. Not an ideal situation.

Steps to reproduce:

Using the tests/example-partial-failure-with-subtests/ test:

1. Add print("User output is captured!") on line 8 of example_partial_failure_with_subtests.py
2. Run ./bin/run.sh example-partial-failure-with-subtests
3. Note that results.json has an entry that looks like this for ExampleSuccessTest.test_abc:

"name": "ExampleSuccessTest.test_abc",
      "status": "pass",
      "test_code": "input_data = ['frog', 'fish', 'coconut', 'pineapple', 'carrot', 'cucumber', 'grass', 'tree']\nresult_data = [(\"Hello, World!\", param) for param in input_data]\nnumber_of_variants = range(1, len(input_data) + 1)\n\nfor variant, param, result in zip(number_of_variants, input_data, result_data):\n    with self.subTest(f\"variation #{variant}\", param=param, result=result):\n        self.assertEqual(hello(param), result,",
      "task_id": 1,
      "output": "User output is captured!\nUser output is captured!\nUser output is captured!\nUser output is captured!\nUser output is captured!\nUser output is captured!\nUser output is captured!\nUser output is captured!"
    }

Ideally, we'd write captured output for a subtest into the output property for that subtest. In cases where there is not a subtest report (pytest only reports failed subtests), we would annotate the parent test output to indicate it came from a successful subtest.