skip_level_upgrade.js tests that attempting to startup a latest binary node with old LTS data files will fail and will not corrupt the old datafiles. We currently only run this test against v5.0 — we should add v6.0 here.

We should also consider the following investigation in this ticket: is there a way to automate this list so that we don't have to modify it every LTS release? It's easy to forget to append new versions to the test list, and I wasn't sure if there was a programmatic way to get the old LTS versions. see comment