Try to close luks volume before openning

src/scripts/backup_nocloud.sh

@@ -304,6 +304,7 @@ do_log "démarrage le `date`"
 
 if $luks
 then
+    cryptsetup luksClose $luksname
     echo $ENCPASS | cryptsetup luksOpen $dev $luksname
     test_and_fail $? "Impossible de déchiffrer le disque, abandon"
     /bin/mount -t auto /dev/mapper/$luksname $dest