Make health check failures report their reasons

Note that we add a new block with expanded service info, to avoid breaking compatibility with existing callers of the health endpoint

health/healthcheck.py

@@ -46,15 +46,29 @@ class HealthCheck(object):
     is_healthy = True
     notes = notes or []
 
+    service_statuses_bools = {}
+    service_status_expanded = {}
+
     for service_name in service_statuses:
+      status, err = service_statuses[service_name]
+
+      service_statuses_bools[service_name] = status
+      service_status_expanded[service_name] = {
+        'status': status,
+      }
+
+      if not status:
+        service_status_expanded[service_name]['failure'] = err
+
       if skip and service_name in skip:
         notes.append('%s skipped in compute health' % service_name)
         continue
 
-      is_healthy = is_healthy and service_statuses[service_name]
+      is_healthy = is_healthy and status
 
     data = {
-      'services': service_statuses,
+      'services': service_statuses_bools,
+      'services_expanded': service_status_expanded,
       'notes': notes,
       'is_testing': self.app.config['TESTING'],
       'config_provider': self.config_provider.provider_id,