logging: Switch various logging code paths to use user IDs.

This fixes EMAIL_ADDRESS_VISIBILITY_ADMINS support as well as being
more reliable/stable over time.

zerver/lib/transfer.py

@@ -25,7 +25,7 @@ def transfer_avatars_to_s3(processes: int) -> None:
         try:
             with open(file_path, 'rb') as f:
                 s3backend.upload_avatar_image(f, user, user)
-                logging.info("Uploaded avatar for {} in realm {}".format(user.email, user.realm.name))
+                logging.info("Uploaded avatar for {} in realm {}".format(user.id, user.realm.name))
         except FileNotFoundError:
             pass
         return 0