[ci][docker] Prune all non-relevant images

Before this would leave around any image that could be used in CI. This
PR changes it so that the `docker rmi` knows exactly which image is
being used in CI so all others (even those that are being used in the
same build but not currently on that node) are deleted

This also adds some more logging so we can see what's going on and
should help keep disk usage down.

Author: driazati