The remote requests made by the docker-build-step plugin to the docker host have an invalid path, you get 404 response only.

The plugin produces:

http://my.docker.host:4243/v/xyz

Valid request URIs would be:

http://my.docker.host:4243/v1.14/xyz
http://my.docker.host:4243/xyz

Obviously the workaround is to specify a version number in the plugin configuration in the Advances settings.