Fix most tests in Python3.
This set of commit fixes all tests in Python 3 except lib/tests/test_zodb.py::test_zstor_2zurl, which requires support for Python 3 in NEO.
It requires that Pygolang has the changes in https://lab.nexedi.com/nexedi/pygolang/-/merge_requests/21 incorporated.
Edited by Carlos Ramos Carreño