Fix block detail updating (#11015)

* Add finality parameter to `null engine`

* Add testcase for finalization marking in `ethcore` client

* Add double cache read for db

* Prevent lost update of block details

* Read with pending update for block details in batch

json/src/spec/null_engine.rs

@@ -25,6 +25,8 @@ use uint::Uint;
 pub struct NullEngineParams {
 	/// Block reward.
 	pub block_reward: Option<Uint>,
+	/// Immediate finalization.
+	pub immediate_finalization: Option<bool>
 }
 
 /// Null engine descriptor