zope4: Configure logging similarly to what ZConfig used to do.

zope.conf of Zope2 (zopeschema.xml) used to define event/Z2 log files and
properly configure logging but this is not the case anymore with
Zope4 (wsgischema.xml).

This adds path to event/Z2 log files as command line parameter as we probably
don't need further configuration such as message format (SlapOS recipe has never
handled it anyway).