Screen session improved

We can now use simple command to manage ElasticSearch instance inside VMs:

* `node-start`: starts the ElasticSearch instance
* `node-stop`: stops the ElasticSearch instance
* `node-restart`: restarts the ElasticSearch instance
* `node-status`: displays ElasticSearch instance's status
* `node-attach`: brings the user to the screen session hosting the ElasticSearch instance.