Fix [36454] to bypass a bug on Zope 2.8

On old versions of ZODB, DemoStorage.new_oid method requires base storage to be
writable.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@36456 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/tests/custom_zodb.py

@@ -108,7 +108,9 @@ while not zeo_client:
   if save:
     Storage = FileStorage(data_fs_path)
   elif load:
-    Storage = DemoStorage(base=FileStorage(data_fs_path, read_only=True))
+    Storage = FileStorage(data_fs_path, read_only=True)
+    Storage._is_read_only = False # XXX for Zope 2.8
+    Storage = DemoStorage(base=Storage)
   else:
     Storage = DemoStorage()
   break