Make node exporter password default to None.
Created by: smarnach
We've changed the default password in https://github.com/open-craft/ansible-secrets/pull/14 to the much more sensible value None, so we need to change it here as well.
Created by: smarnach
We've changed the default password in https://github.com/open-craft/ansible-secrets/pull/14 to the much more sensible value None, so we need to change it here as well.