save file block allocations in target_files

make_ext4fs can now output a file listing the blocks used for each
file in the image.  Request this file and save it in the target_files;
it will be used for future improvements to block OTAs.

Bug: 16984795
Change-Id: Id1e60465e3b5a9d126a7934b4d089cf34d8fec44

tools/releasetools/img_from_target_files.py

@@ -90,6 +90,7 @@ def main(argv):
       if images:
         for i in images:
           if bootable_only and i not in ("boot.img", "recovery.img"): continue
+          if not i.endswith(".img"): continue
           with open(os.path.join(images_path, i), "r") as f:
             common.ZipWriteStr(output_zip, i, f.read())
         done = True