Support for custom BroadcastStage in local cluster tests (#4716)

* Refactor BroadcastStage to support custom implementations, add FailEntryVerificationBroadcastRun implementation

* Plumb switch on broadcast type through validator

* Add test for validator generating non-verifiable entries to local_cluster

* Fix bad initializers

* Refactor broadcast run code into utils

core/src/tpu.rs

@@ -3,7 +3,7 @@
 
 use crate::banking_stage::BankingStage;
 use crate::blocktree::Blocktree;
-use crate::broadcast_stage::BroadcastStage;
+use crate::broadcast_stage::{BroadcastStage, BroadcastStageType};
 use crate::cluster_info::ClusterInfo;
 use crate::cluster_info_vote_listener::ClusterInfoVoteListener;
 use crate::fetch_stage::FetchStage;
@@ -37,6 +37,7 @@ impl Tpu {
         broadcast_socket: UdpSocket,
         sigverify_disabled: bool,
         blocktree: &Arc<Blocktree>,
+        broadcast_type: &BroadcastStageType,
         exit: &Arc<AtomicBool>,
     ) -> Self {
         cluster_info.write().unwrap().set_leader(id);
@@ -70,7 +71,7 @@ impl Tpu {
             verified_vote_receiver,
         );
 
-        let broadcast_stage = BroadcastStage::new(
+        let broadcast_stage = broadcast_type.new_broadcast_stage(
             broadcast_socket,
             cluster_info.clone(),
             entry_receiver,