Add a USE flag for including kubeadm

BUG=b/187054409
TEST=presubmit
RELEASE_NOTE=None

Change-Id: Ifabac70bb7a82dc89eca760484e75a62e13e2782
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/16270
Reviewed-by: Roy Yang <royyang@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
4 files changed