clean for docker build
at the moment, when we build docker, we copy everything that's in the node directory into the docker image.
if you have some errant files in there, they get copied up to - there is no clean
I believe we should create a tmp build dir under there in which we copy:
- everything that we need from node
- everything that we need from elsewhere
then we should blow away the build dir on clean
you can lose a lot of time to this!