daily 150.clean-hoststat: suppress error when using dma

dma(8) does not have hoststat or purgestat, so this script produces
an error from the daily script.  We could disable this script, but
that would mean yet another change to switch back to sendmail.  Check
for purgestat in mailer.conf before attempting either hoststat or
purgestat.

Reviewed by:	pstef, bapt
Differential Revision:	https://reviews.freebsd.org/D37712

usr.sbin/periodic/etc/daily/150.clean-hoststat

@@ -2,7 +2,7 @@
 #
 # $FreeBSD$
 #
-# Remove stale persistent host status files
+# Remove stale persistent host status files if the mailer supports it.
 #
 
 # If there is a global system configuration file, suck it in.
@@ -14,7 +14,9 @@ fi
 
 case "$daily_clean_hoststat_enable" in
     [Yy][Ee][Ss])
-	if [ -z "$(hoststat 2>&1)" ]; then
+	if ! grep -q '^purgestat' /etc/mail/mailer.conf; then
+	    rc=3
+	elif [ -z "$(hoststat 2>&1)" ]; then
 	    rc=2
 	else
 	    echo ""