Fixed Chef Zero usage and environment files

When trying out the deployment I stumbled upon some invalid JSON in the README and the actual environment file (zero-demo.json). Also, some commands were wrong/outdated in the README for the Chef Zero usage.

I also updated the vagrant-multi-neutron.json with a working configuration. I verified the vagrant-multi-neutron.json with a Chef Server deployment and the Vagrantfile-multi-neutron deployment. It did not work with the old version.