Add AUTOTESTS_ADDON flag to set additional tests

COS has the need to set additional autotests based on feature set. So we
define a environmental variable AUTOTESTS_ADDON to help reach the goal.

BUG=b/291595249
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I34273da61b8f3c7ba5166368d81776721f01059c
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/72556
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: RBE-prod-presubmit <service-269995278450@remotebuildexecution.iam.gserviceaccount.com>
1 file changed