Migrate unikernel builds to cluster

[talex5]

I've moved all the Docker services from the old deployer on toxis to the new one on ci3.

The only thing the old service is still doing is deploying the unikernels. This code is now on the old-master branch.

The old service builds the unikernels locally with Docker and then rsyncs to the host. However, the new deployer host isn't suitable for building things. Instead, it should use the cluster. We need to decide how to get the resulting binaries from the workers to the host.

Some options:

1. Push to Docker hub and have the unikernel host pull them (requires Docker on the host though).
2. Have the worker transfer directly to the host (will probably want some kind of short-lived session key for the transfer).
3. Transfer from the worker to the deployer and rsync from there as before. Avoids having to make changes on the unikernel host.

@hannesm do you have a preference here? I think you mentioned that you were planning some kind of unikernel registery which we could push to...