Make scripts/update_payload available for other python modules

The new merge_ota tool will need this module to read/write OTA packages

Test: th
Bug: 227848550

Change-Id: Ibfe2fca65ffbaca939ea3f8ca924c9152e5e7540
diff --git a/scripts/update_payload/test_utils.py b/scripts/update_payload/test_utils.py
index e153669..7005827 100644
--- a/scripts/update_payload/test_utils.py
+++ b/scripts/update_payload/test_utils.py
@@ -27,7 +27,7 @@
 
 from update_payload import common
 from update_payload import payload
-from update_payload import update_metadata_pb2
+import update_metadata_pb2
 
 
 class TestError(Exception):