Select the full RepositoryBuild record

If we just return the ID, then peewee just fills in the other fields with defaults (such as UUID).

data/model/build.py

@@ -175,11 +175,12 @@ def get_archivable_build():
           .alias('candidates'))
 
   try:
-    return (RepositoryBuild
+    found_id = (RepositoryBuild
              .select(candidates.c.id)
              .from_(candidates)
              .order_by(db_random_func())
              .get())
+    return RepositoryBuild.get(id=found_id)
   except RepositoryBuild.DoesNotExist:
     return None