new_variant: clean EC before testing

Stale output files in the EC build directory can cause intermittent
build failures. Clean the EC build before starting the new variant.

BUG=b:168755528
TEST=`testdata/new_variant_fulltest.sh waddledee &&
testdata/new_variant_fulltest.sh waddledoo && echo PASS`
After building new variants of both reference boards, you'll see
a "PASS" as the last line of output.

Change-Id: I602db6e6dc629a7e19687a6367e6cc2976c194e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2426247
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Auto-Submit: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Karthikeyan Ramasubramanian <kramasub@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
1 file changed