cfgupgrade: really ignore hostname when told so

cfgupgrade provides a --ignore-hostname option, however consequently it
spawns config.ConfigWriter, which refuses to handle a foreign
configuration file by default.

config.ConfigWriter provides a relative keyword argument,
accept_foreign, so we tie this to the value of options.ignore_hostname.

Signed-off-by: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

tools/cfgupgrade

@@ -221,6 +221,7 @@ def main():
   if not (options.dry_run or options.no_verify):
     logging.info("Testing the new config file...")
     cfg = config.ConfigWriter(cfg_file=options.CONFIG_DATA_PATH,
+                              accept_foreign=options.ignore_hostname,
                               offline=True)
     # if we reached this, it's all fine
     vrfy = cfg.VerifyConfig()