Proposal: Containerized jenkins-slave

Containerized the jenkins slave to allow moving slaves easily between clouds / environments.

As I don't have NODE_NAME and NODE_SECRET I could only test whether the container builds and not the actual test running. Most steps are copied from https://github.com/deis/deis/blob/master/tests/bin/setup-node.sh

@mboersma I'm not sure how you imagined the AWS CI setup, but I thought having a CoreOS cluster and jenkins-slaves deployed using fleet is the nicest way. If you like this approach I could look into the missing components (dev-registry start? containerize and link postgres)