slapos.libnetworkcache does not use python reserved file anymore.

src/zc/buildout/networkcache.py

@@ -113,7 +113,7 @@ def upload_network_cached(dir_url, cache_url, external_url, path, logger,
     file_name = get_filename_from_url(external_url)
 
     directory_key = get_directory_key(external_url)
-    kw = dict(file=file_name,
+    kw = dict(file_name=file_name,
               urlmd5=hashlib.md5(external_url).hexdigest())
     signature_certificate_file_list = signature_certificate_file.split('\n')