Executable queue for ancient blocks inclusion (#208)

* Executable queue for ancient blocks inclusion
* Add drop trait for client
* Added shutdown to tests
* Remove doubled call
* Use reth-util from reth repo

crates/ethcore/src/json_tests/chain.rs

@@ -232,6 +232,7 @@ pub fn json_chain_test<H: FnMut(&str, HookType)>(
                     client.chain_info().best_block_hash == blockchain.best_block.into()
                         && post_state_success,
                 );
+                client.shutdown()
             }
         }