Stream entries (#2582)

* Add entry streaming option

* Fix tests

* Remove obsolete comment

* Move entry stream functionality to struct w/ trait in order to test without i/o

tests/replicator.rs

@@ -61,6 +61,7 @@ fn test_replicator_startup() {
             ))),
             None,
             STORAGE_ROTATE_TEST_COUNT,
+            None,
         );
 
         let validator_keypair = Arc::new(Keypair::new());
@@ -91,6 +92,7 @@ fn test_replicator_startup() {
             ))),
             None,
             STORAGE_ROTATE_TEST_COUNT,
+            None,
         );
 
         let bob = Keypair::new();
@@ -287,6 +289,7 @@ fn test_replicator_startup_ledger_hang() {
             None,
             false,
             None,
+            None,
         );
 
         let validator_keypair = Arc::new(Keypair::new());
@@ -304,6 +307,7 @@ fn test_replicator_startup_ledger_hang() {
             Some(&leader_info),
             false,
             None,
+            None,
         );
 
         info!("starting replicator node");