swarmbucket: add $project template parameter

appengine/cr-buildbucket/config.py

Index: appengine/cr-buildbucket/config.py
diff --git a/appengine/cr-buildbucket/config.py b/appengine/cr-buildbucket/config.py
index 7af4e45c4483e43f1a08b88f096a41d7947aae49..515dcebbd8eed4a662e59362be369448b97fdadd 100644
--- a/appengine/cr-buildbucket/config.py
+++ b/appengine/cr-buildbucket/config.py
@@ -140,11 +140,12 @@ def get_buckets_async():
 @ndb.non_transactional
 @ndb.tasklet
 def get_bucket_async(name):
-  """Returns a project_config_pb2.Bucket by name."""
+  """Returns a (project, project_config_pb2.Bucket) tuple."""
   bucket = yield Bucket.get_by_id_async(name)
   if bucket is None:
-    raise ndb.Return(None)
-  raise ndb.Return(parse_bucket_config(bucket.config_content))
+    raise ndb.Return(None, None)
+  raise ndb.Return(
+      bucket.project_id, parse_bucket_config(bucket.config_content))
 
 
 def cron_update_buckets():