servo: transmission: torrent-done: fix dry-run; ensure all destructive ops are actually marked as destructive

hosts/by-name/servo/services/transmission/torrent-done

@@ -1,11 +1,16 @@
 #!/usr/bin/env nix-shell
 #!nix-shell -i bash -p acl -p bash -p coreutils -p findutils -p rsync -p util-linux
 
+# transmission invokes this with no args, and the following env vars:
+# - TR_TORRENT_DIR: full path to the folder i told transmission to download it to.
+#     e.g. /var/media/torrents/Videos/Film/Jason.Bourne-2016
+# optionally, perform a dry run by setting TR_DRY_RUN=1
+
 DOWNLOAD_DIR=/var/media/torrents
 
 destructive() {
   if [ -n "${TR_DRY_RUN-}" ]; then
-    echo "$*"
+    echo "[dry-run] $*"
   else
     "$@"
   fi
@@ -34,12 +39,12 @@ subdirs=("$MEDIA_DIR"/*)
 if [ ${#subdirs} -eq 1 ]; then
   dirname="${subdirs[0]}"
   if [ -d "$dirname" ]; then
-    mv "$dirname"/* "$MEDIA_DIR/" && rmdir "$dirname"
+    destructive mv "$dirname"/* "$MEDIA_DIR/" && destructive rmdir "$dirname"
   fi
 fi
 
 # remove noisy files:
-find "$MEDIA_DIR/" -type f \(\
+destructive find "$MEDIA_DIR/" -type f \(\
      -iname '.*downloaded.?from.*' \
   -o -iname 'source.txt' \
   -o 'iname 'upcoming.?releases.*' \