bug 1166263 image-update handling for closed stdin

handles the case where an image-update command is issued from a cron job with an
invalid standard input file descriptor: consider no image data is provided when
no --file option present.

Change-Id: I5eb3433311e5faf0a3fb7eb36f6a01e5df7efe4c
Merge "bug 1166263 image-update handling for closed stdin"