EZP-23441: Tweaked IO setup of legacy tests

1. Made sure that vardir cleanup and data init are in sync

2. Reordered tests in BaseIntegrationTest: the test update with no change
was done between testUpdate and its data test methods. This was resetting
the repository. It doesn't matter for most tests, but it does for image test:
when testing the updated data, we need the vardir to be untouched after
update.