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

bench-exchange/src/bench.rs

@@ -963,7 +963,6 @@ mod tests {
         solana_logger::setup();
 
         const NUM_NODES: usize = 1;
-        let validator_config = ValidatorConfig::default();
 
         let mut config = Config::default();
         config.identity = Keypair::new();
@@ -985,7 +984,7 @@ mod tests {
         let cluster = LocalCluster::new(&ClusterConfig {
             node_stakes: vec![100_000; NUM_NODES],
             cluster_lamports: 100_000_000_000_000,
-            validator_config,
+            validator_configs: vec![ValidatorConfig::default(); NUM_NODES],
             native_instruction_processors: [solana_exchange_program!()].to_vec(),
             ..ClusterConfig::default()
         });