futility: Let each command provide its own help

Instead of a separate help function for each command, let's just
require each command to handle a --help option. This will make it
easier to layer the commands (for example, "sign" could have
several subcommand variants, each with its own help).

BUG=none
BRANCH=none
TEST=make runtests

I also compared the result of running "futility help CMD" before
and after this change. The help still shows up correctly.

Change-Id: I5c58176f32b41b0a2c2b8f0afb17dddd80fddc70
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/260495
Reviewed-by: Randall Spangler <rspangler@chromium.org>
15 files changed