Fix pylint issue in payload.py

    ************* Module update_payload.payload
    W: 12, 0: Relative import 'applier', should be 'update_payload.applier' (relative-import)
    W: 13, 0: Relative import 'block_tracer', should be 'update_payload.block_tracer' (relative-import)
    W: 14, 0: Relative import 'checker', should be 'update_payload.checker' (relative-import)
    W: 15, 0: Relative import 'common', should be 'update_payload.common' (relative-import)
    W: 16, 0: Relative import 'error', should be 'update_payload.error' (relative-import)
    W: 17, 0: Relative import 'update_metadata_pb2', should be 'update_payload.update_metadata_pb2' (relative-import)
    C:222, 4: Missing function docstring (missing-docstring)
    E:261,33: Instance of 'DeltaArchiveManifest' has no 'partitions' member (no-member)

Test: repo upload
Change-Id: Ib3e99c6a3a5ea4575b442e672a871adc7b985289
diff --git a/pylintrc b/pylintrc
index f264479..80a7605 100644
--- a/pylintrc
+++ b/pylintrc
@@ -149,7 +149,7 @@
 # (useful for modules/projects where namespaces are manipulated during runtime
 # and thus existing member attributes cannot be deduced by static analysis. It
 # supports qualified module names, as well as Unix pattern matching.
-ignored-modules=
+ignored-modules=update_payload.update_metadata_pb2
 
 # List of classes names for which member attributes should not be checked
 # (useful for classes with attributes dynamically set). This supports can work