Use the new random interval support in cron instead of a random sleep.

The random intervals used can be adjusted as needed.  OK deraadt@

src/etc/crontab

@@ -1,4 +1,4 @@
-#	$OpenBSD: crontab,v 1.25 2019/12/04 15:07:51 job Exp $
+#	$OpenBSD: crontab,v 1.26 2020/04/15 03:24:08 millert Exp $
 #
 # /var/cron/tabs/root - root's crontab
 #
@@ -17,6 +17,6 @@ HOME=/var/log
 30	1	*	*	*	/bin/sh /etc/daily
 30	3	*	*	6	/bin/sh /etc/weekly
 30	5	1	*	*	/bin/sh /etc/monthly
-#0	*	*	*	*	sleep $((RANDOM \% 2048)) && /usr/libexec/spamd-setup
+#~	*	*	*	*	/usr/libexec/spamd-setup
 
-#0	9	*	*	*	-n sleep $((RANDOM \% 4096)) && rpki-client -v && bgpctl reload
+#0~20	9	*	*	*	-n rpki-client -v && bgpctl reload