serve.py: fix issue with nagios check when using threshold checks or when showing critical status

ligo/scald/serve.py

@@ -429,13 +429,13 @@ def serve_nagios(check):
     if bad_status:
         if alert_type == 'heartbeat':
             text_status = "{num_tags} {alert_tag} more than {lookback} seconds behind".format(
-                alert_tag=nagios_config['alert_settings']['tag_key'],
+                alert_tag=schema['tag_key'],
                 num_tags=bad_status,
                 lookback=duration,
             )
         elif alert_type == 'threshold':
             text_status = "{num_tags} {alert_tag} above {column} threshold = {threshold} {units} from gps times: {start} - {end}".format(
-                alert_tag=nagios_config['alert_settings']['tag_key'],
+                alert_tag=schema['tag_key'],
                 threshold=nagios_config['alert_settings']['threshold'],
                 units=nagios_config['alert_settings']['threshold_units'],
                 num_tags=bad_status,
@@ -449,7 +449,7 @@ def serve_nagios(check):
             text_status = "OK: Max delay: {delay} seconds".format(delay=max(alert_values))
         elif alert_type == 'threshold':
             text_status = "OK: No {alert_tag}s above {column} threshold = {threshold} {units} from gps times: {start} - {end}".format(
-                alert_tag=nagios_config['alert_settings']['tag_key'],
+                alert_tag=schema['tag_key'],
                 threshold=nagios_config['alert_settings']['threshold'],
                 units=nagios_config['alert_settings']['threshold_units'],
                 column=measurement,