test: refactor test_runner tests to change default reporter
This commit updates the test runner tests in order to switch the default reporter from tap to spec. This commit can be backported, while changing the default reporter cannot.
This will also allow us to more slowly migrate the tests off of using the TAP reporter in some places. We should still test the TAP reporter though. In some cases the TAP reporter is beneficial for testing purposes - for example, verifying that tests are output with the correct test number ordering.