This command can be used to create or manage the ZooKeeper ensemble for Fuse Fabric.
There are four different usages:

* fabric:ensemble-list
The list of agents composing the current ensemble will be displayed.

* fabric:ensemble-create [list of agents]
This mode will create a new ensemble composed of the given agents and will switch all agents to this new ensemble.

* fabric:ensemble-add [list of agents]
This mode will add the given agents to the ensemble. All agents will be switched to this new ensemble.

* fabric:ensemble-remove [list of agents]
This mode will create a new ensemble composed of the existing agents excluding the agents specified on the command line. All agents will be switched to this new ensemble.

Note that given ZooKeeper is the key component of Fabric, changing the ZooKeeper ensemble is a critical operation.  All data will be preserved and copied to the new ensemble before swichting.
