If two jobs are pulling the same image simultaneously, which ever starts the pull first will set the pull timeout.
This can lead to a poor UX where the first job requested a short timeout while the second job requested a longer timeout
causing the pull to potentially timeout much sooner than expected by the second job.
This PR introduces a coordinator for doing CRUD on a Docker image. It
should fix racy deletion of images. The issue before was images would be
deleted between prestart and start causing an error.
Nick Ethier