security test: Add test that verifies that update verification is enabled

BUG=chromium-os:31893
TEST=verified on images with/without payload verification enabled.

Change-Id: Ic1883aafcc2c48d9e7c5323d6dc7e21fb8f47585
Reviewed-on: https://gerrit.chromium.org/gerrit/25407
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
4 files changed