Jib should avoid parallel image downloads for same image

Although jib is thread-safe, it should be smarter.

Jib doesn’t currently lock the base image cache when downloading a base image, but instead downloads into a temporary directory and then attempts to moves the downloaded image into place. There is no locking to block other threads. So a Maven project with N modules that build images using the same base image (like gcr.io/distroless/java) may result in N simultaneous pulls of the same image. Maybe we should provide a component to centralize downloading images?

_Originally posted by @briandealwis in https://github.com/GoogleContainerTools/jib/issues/1904#issuecomment-521352655_

[chanseokoh]

And this only matters when you enable the Maven parallel builds (-T <thread counts>) or run multiple Jib processes simultaneously on the same host. (And only when the base image layers have never been cached.) Does not affect correctness even in those cases.

[TadCordle]

That is true, but when you don’t target a registry, Jib still caches base images locally to skip unnecessary pulls. So I think this issue is really only a problem for clean multi-module builds.