This patch enhances the ERP5 + WCFS integration tests. Before it was
only minimal; now it runs actual workload of writing and reading
ZBigArray to the ZODB. This is necessary to securely verify WC2 is
working with ERP5.

We had to implement the new tests in a separate test environment,
because SlapOS Integration tests run with python3, but we need python2
for NEO support. We need NEO, because we want to test if WCFS works with
NEO client.