[autotest] Frontend job is not forwared to its shard

frontend.afe.models.Job.assign_to_shard() had a bug.

BUG=chromium:508697
TEST=puppylab. Create a frontend job to a shard host.

Change-Id: I5218af68dff3531202c25b1f960766b8f810970b
Reviewed-on: https://chromium-review.googlesource.com/284674
Trybot-Ready: Mungyung Ryu <mkryu@google.com>
Tested-by: Mungyung Ryu <mkryu@google.com>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Mungyung Ryu <mkryu@google.com>
diff --git a/frontend/afe/models.py b/frontend/afe/models.py
index 844ee6d..699eddf 100644
--- a/frontend/afe/models.py
+++ b/frontend/afe/models.py
@@ -1559,10 +1559,9 @@
             check_known_jobs_include = 'OR ' + check_known_jobs
 
         for sql in [cls.SQL_SHARD_JOBS, cls.SQL_SHARD_FRONTEND_JOBS]:
-            query = Job.objects.raw(
-                    cls.SQL_SHARD_JOBS %
-                    {'check_known_jobs': check_known_jobs_exclude,
-                     'shard_id': shard.id})
+            query = Job.objects.raw(sql % {
+                    'check_known_jobs': check_known_jobs_exclude,
+                    'shard_id': shard.id})
             job_ids |= set([j.id for j in query])
 
         if job_ids: