Add missing local API down alert

Change-Id: If6f733e4d67e5f1fcb03dfd4b83fffce823ba56a
diff --git a/heat/meta/prometheus.yml b/heat/meta/prometheus.yml
index a8dee85..f72af6a 100644
--- a/heat/meta/prometheus.yml
+++ b/heat/meta/prometheus.yml
@@ -16,6 +16,17 @@
         summary: "Endpoint check for '{{ $labels.service }}' is down"
         description: >-
             Endpoint check for '{{ $labels.service }}' is down for 2 minutes
+    HeatAPIServiceDown:
+      if: >-
+        http_response_status{service=~"heat.*-api"} == 0
+      for: 2m
+      labels:
+        severity: down
+        service: "{{ $labels.service }}"
+      annotations:
+        summary: "HTTP check for '{{ $labels.service }}' down"
+        description: >-
+            The HTTP check for '{{ $labels.service }}' is down on {{ $labels.host }} for 2 minutes.
     HeatErrorLogsTooHigh:
 {%- endraw %}
       {%- set log_threshold = monitoring.error_log_rate|float %}