Extend the upgrade tests to create data before the upgrade, to
confirm that this data can still be found after the upgrade.

This also extends the test to confirm that after upgrade, inituser
can still login, create content and find content created before and
after upgrade.

After 4fa33dfc (erp5: py3: `func_{code,defaults}` was replaced in
Python3 by `__{code,defaults}__`., 2022-04-25), this was no longer
the case, because during indexation, using existing scripts failed
with AttributeError __code__