Don't require increased open file limit in solana-test-validator

Travis CI in particular does not allow the open file limit to be
increased.

local-cluster/tests/local_cluster.rs

@@ -1663,11 +1663,10 @@ fn test_validator_saves_tower() {
 }
 
 fn open_blockstore(ledger_path: &Path) -> Blockstore {
-    Blockstore::open_with_access_type(ledger_path, AccessType::PrimaryOnly, None).unwrap_or_else(
-        |e| {
+    Blockstore::open_with_access_type(ledger_path, AccessType::PrimaryOnly, None, true)
+        .unwrap_or_else(|e| {
             panic!("Failed to open ledger at {:?}, err: {}", ledger_path, e);
-        },
-    )
+        })
 }
 
 fn purge_slots(blockstore: &Blockstore, start_slot: Slot, slot_count: Slot) {
@@ -1887,6 +1886,7 @@ fn do_test_optimistic_confirmation_violation_with_or_without_tower(with_tower: b
                 &val_a_ledger_path,
                 AccessType::TryPrimaryThenSecondary,
                 None,
+                true,
             )
             .unwrap();
             let mut ancestors = AncestorIterator::new(last_vote, &blockstore);