fix test condition to delete cache

Dockerfiles/python/scripts/launch.sh

@@ -110,7 +110,7 @@ if [ $action == "cleanup"  ] || [ $action == "all"  ]; then
   check
 
   comment "Cleanup tiles cache"
-  [[ -d $cache_dir ]] && find $cache_dir -name "*.png" -exec rm -f {} \;
+  [ -f "$cache_dir/*.png" ] && find $cache_dir -name "*.png" -exec rm -f {} \;
   check
 fi