Dockerfile image derivation

[pdmack]

Docker 17.05 introduced multi-builder support which means that the oshinko s2i docker files could essentially be composed piecemeal from multiple images. For example:

FROM radanalyticsio/openshift-spark:2.2-latest
FROM fabric8/s2i-java:latest AS fabric8-builder
....
WORKDIR /usr/local/s2i/
COPY --from=fabric8-builder /usr/local/s2i/* .

Only catch is that the version available for our "current platforms" is 1.12.