Support building and publishing Docker images.

This provides reasonable behaviour for Docker publish/publishLocal tasks.
docker:publishLocal maps to "docker build -t [dockerTarget] ."
docker:publish maps to "docker push -t [dockerTarget]"
docker:dockerTarget has a default value of [dockerRepository]/[normalizedName]:[version]
Add scripted test that a basic Docker image is built by publishLocal
Merge pull request #277 from garycoady/wip/docker-publish

Support building and publishing Docker images.