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.
1: I forgot add the return statement if the if statement... The idea is that the next cluster update will trigger the IndicesStore logic again, so I think we don't need to trigger once shards have moved around?
2: So setting the IndexShard instance in ShardActiveResponseHandler and then upon removing if the instance is the same as the current one?