external chaincode buildpack

This produces a small luthersystems/buildpack docker image artifact which is intended to be used as an init container for a fabric peer pod running on Kubernetes. The init container and peer container should share an emptyDir volume. A directory on that volume should be supplied as the single argument to the init container and as the location of the external buildpack in the peer core.yaml config. The init container will copy the buildpack scripts into that directory on boot.