Mention the ``end of output'' for each periodic script.

Submitted by:	David Wolfskill <david@catwhisker.org>
PR:		37036
MFC after:	1 week

usr.sbin/periodic/periodic.sh

@@ -97,6 +97,9 @@ do
         then
           [ $processed = 1 ] && plural= || plural=s
           echo "No output from the $processed file$plural processed"
+        else
+          echo ""
+          echo "-- End of $arg output --"
         fi
     } | eval $pipe
 done