Implement test and fix for that case #201

Add test_should_account_for_zero_paddded_keys plus its corresponding fix
for it.

server/lib/python/cartodb_services/cartodb_services/metrics/user.py

@@ -85,6 +85,11 @@ class UserMetricsService:
                                                      service, metric, date)
             score = self._redis_connection.zscore(redis_prefix, date.day)
             aggregated_metric += score if score else 0
+            zero_padded_day = date.strftime('%d')
+            if str(date.day) != zero_padded_day:
+                score = self._redis_connection.zscore(redis_prefix, zero_padded_day)
+                aggregated_metric += score if score else 0
+
         return aggregated_metric
 
     # Private functions