At the moment, the build registry is not used inside Kubernetes jobs
and it is required to override the entire pre.yaml just to enable it.
This patch adds an option of using docker_use_buildset_registry inside
install-docker which can be used in order to install Docker and letting
it use the buildset registry simply by adjusting the job.vars
Change-Id: I1b42eac6accbf7c350aee76d18a823ba6327548d