Similarly to FileStorage, fs1tools and zodbtools previously we were testing
demo only with old FileStorage testdata generated by python2 and pickle
protocol=2. However even on py2 there are more pickle protocols that
are in use, and also there is python3.

-> Adjust demo testing to automatically load and test agains all ZODB
kinds from recently updated FileStorage testdata.

All py2_pickle1, py2_pickle2, py2_pickle3 and py3_pickle3 are handled well out of the box.