Add test for replicator ledger download

Add an interface to query the storage slot a
  replicator is holding on storage_addr port.
Fix logic to poll blocktree for all slots
  replicated being filled.
Add test logic to ask replicator what slot it
  is replicating and then download an entry in
  the slot.

core/src/local_cluster.rs

@@ -196,7 +196,7 @@ impl LocalCluster {
             &replicator_keypair.pubkey(),
             1,
         );
-        let replicator_node = Node::new_localhost_with_pubkey(&replicator_keypair.pubkey());
+        let replicator_node = Node::new_localhost_replicator(&replicator_keypair.pubkey());
 
         let (replicator_ledger_path, _blockhash) = create_new_tmp_ledger!(&self.genesis_block);
         let replicator = Replicator::new(