erp5_scalability_test: enable activity tracking log for deeper diagnostic.

bt5/erp5_scalability_test/SkinTemplateItem/portal_skins/erp5_scalability_test/ERP5Site_setUpActivityTool.py

 if not context.portal_activities.isSubscribed():
   context.portal_activities.subscribe()
 
+context.portal_activities.manage_enableActivityTracking()
 context.portal_activities.manage_removeFromProcessingList(context.portal_activities.getProcessingNodeList())
 
 distribution_node = None