Initial test for ODF files

[thebearon]

Right now the first step is skipped for ODF files, because there's no point in trying to open them in MSO. However, the ODF test files can be equally corrupted, which will inflate the failed conversion stats. Best would be to do an ODF -> ODF roundtrip as first step for them, treat failures as corrupted files, and skip those in the future.

It might be interesting to run those corrupted files through an old LO version (desktop conversion) to verify ODF import/export didn't regress over time.