Use Python 2.5/2.6 compatible syntax with bz2.BZ2File (#10403)

Make OMERO.tables integration tests compatible with Python 2.5 and 2.6:
https://github.com/openmicroscopy/openmicroscopy/pull/728#issuecomment-13545014

Testing: Run tests on a Python 2.5/2.6 system.