Roll for Serf (https://www.serfdom.io/)

This Roll installs Serf on every nodes of the cluster and
configure to use it /etc/serf/ as a source of configuration.
So every file which is droped in that folder with .json
will be read as a configuration file.

Serf uses a global encryption key for compuncation
and a password for local comunication with the agent
The password is also saved in /etc/serf/rpcauth for
convinience.

So to talk to serf you need to:
serf members -rpc-auth=`cat /etc/serf/rpcauth`