stack/erp5/run-zelenium-test.py.in: avoid to make Site Unavailable when launch test
Run wait_for_activities macro in selenium test on erp5 with activity subscribed may end with:
INFO SQLBase Got a lock error, retrying...
.....
WARNING waitress.queue Task queue depth is 1
WARNING waitress.queue Task queue depth is XXX
....
503 Service Unavailable