Like with FileStorage previously we were testing fs1tools only with data
generated by python and pickle protocol=2. However even on py2 there are
more pickle protocols that are in use, and also there is python3.

-> Modernize testdata generation to automatically pick up all ZODB kinds
   from recently-updated FileStorage/go testdata.

   Adjust tests on Go side to verify how fs1tools handles all generated zkinds.

py2_pickle1, py2_pickle2 and py2_pickle3 are handled well.
Tests for py3_pickle3 currently fail and so are marked with "xfail".

We will fix tests for py3_pickle3 in follow-up patches.