This should enable later parts of the pipeline to start as soon as their own
dependencies are satisfied, without waiting for the entire stage to complete.

It's a separate mount anyway, so the mv isn't any better performance than cp + rm

The maven cache might be getting in the way of some of the scanners, so before
they execute, let's move it to its normal place. Later, we have to move it back,
otherwise the cache won't get updated (and might get cleared).

This reverts commit d5cdede6.

Will probably need to revisit this later, in case other cloud providers have Docker images.

This reverts commit b3581272.

Previous approach seems like it was sending a literal "$CI_PROJECT_DIR" to
maven, as though it refused to resolve multiple layers of variables.

This is not used by libraries (or other projects that don't generate
containers), so we don't want it all the time.