CARL should track the state of a cluster

[kKdH]

Currently CARL does not track the state of a cluster. It is currently possible to deploy a cluster but CARL does not track whether the cluster is pending (due to missing peers), healthy and ready to be used or unhealthy/failing. But these information is important for users and external programs and further for test execution.

We have already elaborated a set of states for a cluster here

This issue is heavily related to #7 because the cluster state dependes on the peer state of the peers in question.