erp5_ui_test_core: Generate the correct selenium test URL for the test page

The previous implementation will generate URL like:
erp5/test_page_module/core/TestRunner.html?
Which missed the test created in portal_tests, the correct one should be:
erp5/test_page_module/portal_tests/user-Howto.Create.Persons/core/TestRunner.html?
This code was inspired by https://lab.nexedi.com/nexedi/erp5/blob/master/product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py#L86

bt5/erp5_ui_test_core/SkinTemplateItem/portal_skins/erp5_ui_test_core/Zuite_createAndLaunchSeleniumTest.py

@@ -8,4 +8,6 @@ zuite = context.getPortalObject().portal_tests.Zuite_addZuite(zuite_id)
 for text, title in test_list:
   zuite.Zuite_addTest(None, title, text)
 
-return zuite.Base_redirect("core/TestRunner.html?auto=true&test=..%2Ftest_suite_html&resultsUrl=..%2FpostResults")
+ZELENIUM_BASE_URL = "portal_tests/%s/core/TestRunner.html?auto=true&test=../test_suite_html&resultsUrl=../postResults"
+
+return zuite.Base_redirect(ZELENIUM_BASE_URL % zuite_id)