if not xmlrpc_interface in config file, use localhost as hostname.

marketing_campaign_tracker.py

@@ -46,6 +46,8 @@
             tracker_base = context.get('tracker_base')
             #### TODO hostbame_bu configuration with configure option menu.
             hostname_bu=tools.config.get('xmlrpc_interface')
+            if not hostname_bu:
+                hostname_bu="localhost"
             port_bu=tools.config.get('xmlrpc_port')
             database_bu=cr.dbname
             id_bu= "%s:%s/%s" % (hostname_bu,port_bu,database_bu)