Use crane to speed up image builds

[trevor-dolby-at-ibm-com]

Google's crane tool (docs here) allows the creation of application images by appending a layer to a base image without needing to download the base image locally. This has the potential to speed up Tekton builds by avoiding the buildah/kaniko "download and unpack" stage of the build: crane can simply append the application tar file to the image in the registry.

This will affect Tekton in Minikube and OpenShift, but not Jenkins (which uses docker locally) nor ACEaaS (which requires BAR file uploads). GitHub Actions could be enabled for container builds using crane also, but they do not currently go beyond the Unit Test phase and so are also unaffected at this point.