Update script improvements (#236)
Update script improvements (#236)

* Better approach to determining available variants (Borrowed from generate-stackbrew-library.sh
)
* Better approach for skipping "docs" and other non-docker directories (Borrowed from generate-stackbrew-library.sh)
* Also disables tracing from previous commit.

chorrell/docker-node,pesho/docker-node,nodejs/docker-node,nodejs/docker-node,joyent/docker-node,sirgallifrey/docker-node-test,chorrell/docker-node