[devtools] Fix database creation issues for CubicWebServerTC tests To reproduce (with a purged repo): * python web/test/unittest_web.py MiscOptionsTC * python web/test/unittest_views_xmlrss.py The core issue is that CubicWebServerConfig.default_base_url() is called inside init_config(), which is called during the equivalent of 'db-create'. The '__default_empty_db__' will contain the wrong 'base_url' configuration, thus breaking URLs in the xmlrss tests. Related to #9297611.