Problem

To be able to use this role for golden image being build via Packer, I don't want to set the nomad_node_name via ansible and let nomad use the default hostname of the server when the nomad service starts up. The name config variable isn't required to run the service.

Description

This PR will allow users to set the ansible variable nomad_node_name: null to allow nomad to use the hostname on startup. This will still be backward compatible for the current usage of nomad_node_name