component/ZODB: Fix test-zodb4-wc2.cfg build

Since 2023 ZODB.UnitTest-WC2 was invalidated due to many build failures (https://erp5js.nexedi.net/#/test_suite_module/1208). However we are still using ZODB4-wc2 in production with planned fixups and so it is better to recover that testsuite first before going to apply the fixups.

There were two problems:

1. bootstrap failure due to incomplete py2 setup, and
2. build failure around BTrees/persistent due to mismatch of versions in between egg and git checkout.

Please see individual patches for details.

/cc @jerome, @kazuhiko, @xavier_thompson, @levin.zimmermann