Have the config setup tool automatically prepare the S3 or GCS storage with CORS config

storage/basestorage.py

@@ -54,6 +54,10 @@ class BaseStorage(StoragePaths):
   # Set the IO buffer to 64kB
   buffer_size = 64 * 1024
 
+  def setup(self):
+    """ Called to perform any storage system setup. """
+    pass
+
   def get_direct_download_url(self, path, expires_in=60, requires_cors=False):
     return None