Store: Before deleting shard verify that another node holds an active shard instance

Before removing shard physically from disk verify that another node in the cluster actually holds an active shard instance.
I don't think we need all these counters? we can have awaitingReponses which goes to 0 and a activeCopies one that goes up. We stop when awaitingResponses reaches 0 and delete when activeCopies is what we expect