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

data/buildlogs.py

@@ -120,15 +120,14 @@ class RedisBuildLogs(object):
 
       connection = redis.StrictRedis(**args)
       if not connection.ping() == True:
-        return False
+        return (False, 'Could not ping redis')
 
       # Ensure we can write and read a key.
       connection.set(self._health_key(), time.time())
       connection.get(self._health_key())
-
-      return True
-    except redis.RedisError:
-      return False
+      return (True, None)
+    except redis.RedisError as re:
+      return (False, 'Could not connect to redis: %s' % re.message)
 
 
 class BuildLogs(object):