zope4: Handle log rotation following Zope documentation.

SIGUSR2 for reopening log files was handled by ZServer and waitress does not
handle signals at all, so we could handle this signal but Zope official
documentation recommends using logrotate `copytruncate`:
  https://zope.readthedocs.io/en/4.7/zopebook/MaintainingZope.html#log-rotation
  https://github.com/zopefoundation/Zope/issues/809