get-interface-stats error code to match sensu's expectations

brian_polling_manager/interface_stats/cli.py

@@ -329,8 +329,11 @@ def cli(
         logger.exception(
             f"Error while processing {str(vendor).capitalize()} router {router_fqdn}"
         )
+        # Exit code 2 indicates CRITICAL in Sensu
+        raise click.exceptions.Exit(2)
 
     if error_counter.count:
+        # Exit code 1 indicates WARNING in Sensu
         raise click.ClickException(
             "Errors were encountered while processing interface stats"
         )