futility: updater: Use model name as default whitelabel signature

In Unibuild, the white label models may use (per model) PreMP key for
devices without VPD 'whitelabel_tag' - this helps dogfooders and lab
machines to run and update properly.

TEST=make futil; tests/futility/run_test_scripts.sh $(pwd)/build/futility

Change-Id: I7249e3fb1a2b7ab8ed281d2aa317aee6cde8f8db
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1501614
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
2 files changed