Milestone: Cluster-wide service management

Our current deployment model assumes symmetric clusters, where all services are activated on all nodes and application developers have to deal with deciding which service is actually alive especially in the (common) scenario, where centralized data processing is required.

A typical example is OpenFlow Topology Manager, which needs to talk to all OF switches connected to a cluster and make sense of how they are connected. Such a service typically needs only a failover capability, e.g. ensuring the service runs in the cluster (or its surviving partition).

Forcing all such applications to interact with EOS is an overkill, as they will end up producing essentially-equivalent code all over the ecosystem, with each copy having different issues (because reliable clustering is hard).