Enable mistral-api health check

This patch enables health check execution for mistral api docker container.

Change-Id: I5e2c689c152a21aa12476789d4c64fb71b32d34f
Depends-On: Id10f0d52b1732003533aba6b5c89a5079baba852

docker/services/mistral-api.yaml

@@ -154,6 +154,8 @@ outputs:
             net: host
             privileged: false
             restart: always
+            healthcheck:
+              test: /openstack/healthcheck
             volumes:
               list_concat:
                 - {get_attr: [ContainersCommon, volumes]}