Temporary disable ZServer by default. You can enable it by setting start_zserver environment variable to 1.

The reason is that it always set values to portal_activities.distributingNode and portal_activities._nodes.
Before r28043, this didn't happen if self.tic wasn't called, and some projects expects that these variables are unset.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28054 20353a03-c40f-0410-a6d1-a30d3c3de9de