Emit unknown if unable to open the logfile and detect location

Issue #1

check_nagios/check_nagios_ghostservices

@@ -3,7 +3,29 @@ TMP=`mktemp`
 LAST_HOUR=`date "+%b %e %H:" -d "1 hour ago"`
 CURRENT_HOUR=`date "+%b %e %H:"`
 
-tail -n 2000 /var/log/messages | \
+exit_unknown() {
+	msg="$1"
+
+	echo "${msg}"
+	exit 3
+}
+
+find_nagios_log() {
+	# Try to locate the nagios log, fallback to messages log
+	for log in /var/log/nagios/nagios.log /var/log/nagios3/nagios.log /var/log/messages
+	do
+		if [ -e "${log}" ]; then
+			echo ${log}
+			return 0
+		fi
+	done
+	return 3
+}
+
+LOG=$(find_nagios_log) || exit_unknown "Unable to locate logfile for parsing"
+
+tail -n 1 ${LOG} &> ${TMP} || exit_unknown "Unable to parse logfile: $(cat ${TMP})"
+tail -n 2000 ${LOG} | \
 grep -E "$CURRENT_HOUR|$LAST_HOUR" | \
 grep "Passive check result was received" | \
 grep -i "could not be found"  | \