verity: warn on null-valued keys

BUG=chromium-os:20089
TESTED_ON=Kaen
TEST=Adhoc
'verity mode' should emit "missing value: mode" before the standard usage
message now. So should 'verity mode='.

Change-Id: Ica495d07a84fc1924bea37385cc2439032e5ad66
Signed-off-by: Elly Jones <ellyjones@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/7346
Reviewed-by: David James <davidjames@chromium.org>
1 file changed