Enable CORS checks (#2248)

* Introduce CORS CLI flags.

* Fix test.

substrate/core/service/test/src/lib.rs

@@ -120,6 +120,7 @@ fn node_config<F: ServiceFactory> (
 		execution_strategies: Default::default(),
 		rpc_http: None,
 		rpc_ws: None,
+		rpc_cors: None,
 		telemetry_endpoints: None,
 		default_heap_pages: None,
 		offchain_worker: false,