Add a test of corrupt EC firmware signature A

This test corrupts EC firmware signature A and checks if it reboots into
B. Then signature A is restored and it checks EC reboots into A.

BUG=chrome-os-partner:9188
TEST=Test passed

Change-Id: I0b087d5d5ac6d19c69277acee9f92b4a591868ac
Reviewed-on: https://gerrit.chromium.org/gerrit/23476
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Vic Yang <victoryang@chromium.org>
Commit-Ready: Vic Yang <victoryang@chromium.org>
5 files changed