fix "Ignore bad signature certificates with message"

python 3 compatibility

slapos/libnetworkcache.py

@@ -217,7 +217,7 @@ class NetworkcacheClient(object):
       try:
         loaded_certificate = crypto.load_certificate(crypto.FILETYPE_PEM, certificate)
       except Exception as e:
-        logger.info('Ignored wrong certificate, reason:\n%s, offending certificate:\n%s', e.message, certificate)
+        logger.info('Ignored wrong certificate, reason:\n%s, offending certificate:\n%s', e, certificate)
       self.signature_certificate_list.append(loaded_certificate)
 
   # NetworkcacheClient context manager catches all exceptions and logs them