introduce new config option BACKUP_ARGS to add additional parameters to backup job (like tagging the backup)

new option is set to empty if not specified otherwise.

as suggested in https://github.com/binarybucks/restic-tools/pull/14#issuecomment-359700589

Signed-off-by: Felix Bartels <felix@host-consultants.de>

bin/backup

@@ -54,11 +54,14 @@ do_local_backup () {
 
 	. /etc/backup/local.config
 
+	# define an empty default if BACKUP_ARGS is not set
+	BACKUP_ARGS=${BACKUP_ARGS:-""}
+
         if [[ -x /etc/backup/local.pre ]]; then
         	/etc/backup/local.pre $TARGET
  	fi
 
-	$RESTIC --exclude-file /etc/backup/local.exclude backup --hostname $BACKUP_HOSTNAME $BACKUP_DIR
+	$RESTIC --exclude-file /etc/backup/local.exclude backup --hostname $BACKUP_HOSTNAME $BACKUP_ARGS $BACKUP_DIR
 
         if [[ -x /etc/backup/local.post ]]; then
                 /etc/backup/local.post $TARGET

etc/backup/local.config

@@ -1,3 +1,4 @@
 BACKUP_HOSTNAME="backuphost.example.org"
 BACKUP_DIR="/"
+BACKUP_ARGS="--tag filesystem"
 # HEALTHCHECK_URL="<URL from https://healthchecks.io/checks/ to notify>"