test/ec_sync_test: Add mock test for VB_AUX_FW_NO_DEVICE severity

Add a mock test to handle VB_AUX_FW_NO_DEVICE severity

BUG=chromium:896451
BRANCH=None
TEST=/mnt/host/source/chromite/bin/cros_run_unit_tests
      --board=octopus --packages=chromeos-base/vboot_reference

Change-Id: Ifdabdf3cee1130a8c853d57c278f0e557ebbb96f
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1299994
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>
1 file changed