before, without --only-target-package, we were forcing to build the
images locally. Now we extend it also to that use-case.
Also revisit how we pass by the builder image hash, so it's easier to
read.
This change also re-enables tagging and bulding builder images all the
times.
Previously, we regressed into not tagging build images coming out-of-the
tree, with the unpleasant side-effect of not be able to re-build the
same artifacts for those leaf packages.
b27237b7ff