Support image dependencies

[timothyb89]

In monasca-docker we have kafka and kafka-init. kafka-init depends on kafka.

Currently we can't make changes to both within one PR since it will (may?) try to build kafka-init before it builds kafka, and there's no way to enforce build order.

(note that in this case kafka-init's Dockerfile and kafka's build.yml have both been updated to refer to the same new, unpublished version)

[kornicameister]

Hi @timothyb89, there's quite a lot more here to do, but here's my idea to support dependency build before children. I think that for the sake of the building we would need to also modify in-place the children to be based on new "father" so to speak.