factor out rigging for pushing unsigned busybox image
factor out rigging for pushing unsigned busybox image

Signed-off-by: Riyaz Faizullabhoy <97794a5efeea78234636d4fba0f499c15a92f5e3@docker.com>

redpanda/cli,cpuguy83/cli,ashfall/cli,thaJeztah/cli,docker/cli,docker/cli,dnephin/cli,ashfall/cli,redpanda/cli,dnephin/cli,cpuguy83/cli,thaJeztah/cli