Fix/riak cluster start

There is now an attribute `DynamicCluster.FIRST_MEMBER` that will be set to true if a node is first in a cluster. Also `DynamicCluster.CLUSTER_MEMBER` is true if the node is in a cluster, unset otherwise. Finally, `DynamicCluster.CLUSTER` on a clustered node gives the cluster entity itself, and then `DynamicCluster.FIRST` on that will give the first node entity, so other nodes can use this to find it...