Fix a bug in unsigned OTA generation

Caller expects output_file to contain the final OTA, so we must copy
data into that location. Modifying loca variables isn't enough.

Test: make ota with --no_signing
Change-Id: Id4aaefbc53b4250b7308701493d151f9408f47f1

tools/releasetools/ota_utils.py

@@ -16,6 +16,7 @@ import copy
 import itertools
 import logging
 import os
+import shutil
 import struct
 import zipfile
 
@@ -119,7 +120,7 @@ def FinalizeMetadata(metadata, input_file, output_file, needed_property_files):
 
   # Re-sign the package after updating the metadata entry.
   if OPTIONS.no_signing:
-    output_file = prelim_signing
+    shutil.copy(prelim_signing, output_file)
   else:
     SignOutput(prelim_signing, output_file)