Add payload_hash/metadata_hash to update scripts

This makes debugging signature related OTA problems easier, developers
can easily inspect the actual hashes of an OTA package.

Test: th
Change-Id: Ia7f6e8f313a5fda4dc9f9ee4416fd9c9e9b80d5c
diff --git a/scripts/update_payload/payload.py b/scripts/update_payload/payload.py
index 4abd63e..8771ee4 100644
--- a/scripts/update_payload/payload.py
+++ b/scripts/update_payload/payload.py
@@ -152,6 +152,19 @@
     self.Init()
 
   @property
+  def metadata_hash(self):
+    return self.manifest_hasher.digest()
+
+  @property
+  def payload_hash(self):
+    hasher = hashlib.sha256()
+    self.payload_file.seek(0)
+    hasher.update(self.payload_file.read(self.metadata_size))
+    self.payload_file.seek(self.header.metadata_signature_len, io.SEEK_CUR)
+    hasher.update(self.payload_file.read(self.total_data_length))
+    return hasher.digest()
+
+  @property
   def is_incremental(self):
     return any([part.HasField("old_partition_info") for part in self.manifest.partitions])