build_image: Add deprecation warning message

build_image will be moved to python and the new python script will be
available in chromite/bin/build_image. Rename the existing shell script
and add a deprecation warning for users to switch to the new script.

BUG=b:232002778
TEST=./build_image

Cq-Depend: chromium:3642396
Change-Id: Id3c954059443ab057cbb5e6ec3db25b8616c46d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3642376
Tested-by: Ram Chandrasekar <rchandrasekar@google.com>
Auto-Submit: Ram Chandrasekar <rchandrasekar@google.com>
Commit-Queue: Ram Chandrasekar <rchandrasekar@google.com>
Reviewed-by: Cindy Lin <xcl@google.com>
2 files changed