Signed-off-by: Alex Ellis <alexellis2@gmail.com>

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

This adds support for private docker registries, by adding
an optional `registryAuth` field in the CreateFunctionRequest.
Auth must be passed as base64-encoded basic auth, similar to
how done in Docker file store credentials (~/.docker/config.json).
Credentials are then passed to swarm at service creation.