Use a named screen session to host ElasticSearch
Add commands to manage ES instance
Tweak sudo configuration to preserve some env. variables
Store ES logs in the vagrant synced folder to ease reading it.
Allow the user to override the cluster IP range with CLUSTER_IP_PATTERN env. variable

For example, running: `CLUSTER_IP_PATTERN=192.168.50.%d vagrant status`
will configure the cluster with the `192.168.50.0` network
Fix shell provisioning (broken with merges/rebases)