Add a script to generate builds signed using the official keys.

The script sign_official_build.sh does the appropriate signing depending on whether an ssd, recovery or factory-install image is desired.

Also re-factors some common functionality into common.sh.

BUG=3496
TEST=manual

I haven't had a chance to test this on an actual machine running our firmware but will do that before I actually check-in. Thoughts I'd atleast get this out to get the review going.

Review URL: http://codereview.chromium.org/3066034
3 files changed