futility: Create signatures using vboot 2.0 APIs

Refactor futility to use only vboot 2.0 APIs to create signatures.

BUG=chromium:611535
BRANCH=none
TEST=make runtests

Change-Id: I176e7f424fa556d34d8fe691df5681f1e43210ce
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/356128
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
27 files changed