paycheck: Disambiguate hash error messages.

Before we've been emitting the exact same error message when failing to
verify the hash of either pre- or post-update partition. This prefixes
the partition name with "old" or "new", respectively.

BUG=chromium:510909
TEST=None

Change-Id: Icf302d0a3b26d3f9860c4ccb03dba38493296794
Reviewed-on: https://chromium-review.googlesource.com/286143
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/host/lib/update_payload/applier.py b/host/lib/update_payload/applier.py
index da2af12..5e95156 100644
--- a/host/lib/update_payload/applier.py
+++ b/host/lib/update_payload/applier.py
@@ -491,8 +491,8 @@
     if old_part_file_name:
       # Verify the source partition.
       with open(old_part_file_name, 'rb') as old_part_file:
-        _VerifySha256(old_part_file, old_part_info.hash, part_name,
-                      length=old_part_info.size)
+        _VerifySha256(old_part_file, old_part_info.hash,
+                      'old ' + part_name, length=old_part_info.size)
       new_part_file_mode = 'r+b'
       if self.minor_version == common.INPLACE_MINOR_PAYLOAD_VERSION:
         # Copy the src partition to the dst one; make sure we don't truncate it.
@@ -527,8 +527,8 @@
 
     # Verify the resulting partition.
     with open(new_part_file_name, 'rb') as new_part_file:
-      _VerifySha256(new_part_file, new_part_info.hash, part_name,
-                    length=new_part_info.size)
+      _VerifySha256(new_part_file, new_part_info.hash,
+                    'new ' + part_name, length=new_part_info.size)
 
   def Run(self, new_kernel_part, new_rootfs_part, old_kernel_part=None,
           old_rootfs_part=None):