package/petitboot: use default logfile dir

All the petitboot components assume /var/log/petitboot by default;
pb-console can also put multiple logs there and pb-sos collects that
directory when creating a diagnostic tarball.

Defer to this default when launching pb-discover. If someone wants to
override, let's call the file /etc/default/petitboot which makes more
sense to be shared by all the components.

Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit 12e9643021)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/petitboot/S15pb-discover

@@ -2,12 +2,9 @@
 
 DAEMON="pb-discover"
 PIDFILE="/var/run/$DAEMON.pid"
-LOGFILE="/var/log/$DAEMON.log"
-
-PB_DISCOVER_ARGS="-l $LOGFILE"
 
 # shellcheck source=/dev/null
-[ -r "/etc/default/$DAEMON" ] && . "/etc/default/$DAEMON"
+[ -r "/etc/default/petitboot" ] && . "/etc/default/petitboot"
 
 if [ "$(pb-config debug)" = "enabled" ] ; then
 	PB_DISCOVER_ARGS="$PB_DISCOVER_ARGS --verbose"
@@ -15,6 +12,8 @@ fi
 
 start() {
 	printf 'Starting %s: ' "$DAEMON"
+	mkdir -p /var/log/petitboot
+
 	# shellcheck disable=SC2086 # we need the word splitting
 	start-stop-daemon -S -q -b -p "$PIDFILE" -x "/usr/sbin/$DAEMON" \
 		-- $PB_DISCOVER_ARGS