The image used by the Image Promoter (gcr.io/k8s-testimages/gcb-docker-gcloud:v20190906-745fed4)
is based on busybox, and thus, the sed binary is actually busybox. image-util.sh calls
kube::util::ensure-gnu-sed several times, which ensures that a GNU sed binary exists
(it checks by greping GNU in its --help output). Obviously, it won't match the busybox sed
binary. But the sed usage in image-util.sh is fairly simple, and the busybox sed is sufficient.
This was previously fixed in: #87188, but it was reverted by #87653 as it was failing
on Mac (sed does not exist). This commit fixes that issue as well.
6d3a18b0be