Follow up to persistent tower with tests and API cleaning (#12350) (#12972)

* Follow up to persistent tower

* Ignore for now...

* Hard-code validator identities for easy reasoning

* Add a test for opt. conf violation without tower

* Fix compile with rust < 1.47

* Remove unused method

* More move of assert tweak to the asser pr

* Add comments

* Clean up

* Clean the test addressing various review comments

* Clean up a bit

(cherry picked from commit 54517ea454)

Co-authored-by: Ryo Onodera <ryoqun@gmail.com>

local-cluster/src/local_cluster.rs

@@ -370,6 +370,15 @@ impl LocalCluster {
         validator_pubkey
     }
 
+    pub fn ledger_path(&self, validator_pubkey: &Pubkey) -> std::path::PathBuf {
+        self.validators
+            .get(validator_pubkey)
+            .unwrap()
+            .info
+            .ledger_path
+            .clone()
+    }
+
     fn close(&mut self) {
         self.close_preserve_ledgers();
     }