Pytest cleanup

[takishida]

Migrate existing pytests with the old method to the new method.

The old method:

• All tests are in one single file test_logic.py.
• JSON files, which is to simulate the query outputs, for all checks are stored in the same root test folder, which makes it hard to tell which files are used for which test.
• The actual logic in aci-preupgrade-validation-script.py was modified to feed the simulated data (JSON files) for pytest.

The new method:

• Tests for each check are in its own folder along with the JSON files specifically for the check
• With the monkeypatch fixture from pytest, there is no need to embed codes specific to pytest inside the actual logic of aci-preupgrade-validation-script.py.