Fix "Ignore bad signature certificates with message"

Append loaded_certificate in the try block, so it does not result with
"UnboundLocalError: local variable 'loaded_certificate' referenced before assignment"

slapos/libnetworkcache.py

@@ -216,9 +216,9 @@ class NetworkcacheClient(object):
     for certificate in signature_certificate_list or ():
       try:
         loaded_certificate = crypto.load_certificate(crypto.FILETYPE_PEM, certificate)
+        self.signature_certificate_list.append(loaded_certificate)
       except Exception as e:
         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
   # with INFO severity. This provides a easy way to use a networkcache safely