t_radb.py

Task #10902: refactored many selects on resource_usage into method get_resource_usage_at_or_before. Added logging when we detect that a usage_at_start is not found, then the usages table is rebuild for that resource, and then we search again for usage_at_start. Only if not found again, raise exception. This fixes the test for the bug found on production. Still to do: performance increase for rebuild usage table.