Add 'whitelist' option to compare_images

* `compare_images -t a b -s system -w whitelist.txt` to specify
  whitelist.
* diff.csv is split into two parts:
  - whitelisted_diff.csv: Diffs that are ignored by a whitelist
  - diff.csv: Diffs that are not ignored by any whitelist.
* Add `-c, --check` option to compare_images_and_print.sh
  When this option is specified, compare_images_and_print.sh exits with
  a non-zero status if diff.csv contains any unexpected diffs.

Bug: 144398662
Test: Tested manually by creating two directories that contain common
      files, whitelisted diffing files and not whitelisted diffing files.
Test: ./compare_images_and_print.sh --help
Test: ./compare_images_and_print.sh --check "-t a b -s SYSTEM -i"
Change-Id: Ie80741d08ef5bc245b409b46ee716ae783428a7d
3 files changed