Specify the full path of the logs

This makes it easier to run multiple instances, each one writing to
different files.

redhat/varnish.logrotate

-/var/log/varnish/*.log {
+/var/log/varnish/varnish.log /var/log/varnish/varnishncsa.log {
     missingok
     notifempty
     sharedscripts