Fix telemetry panic error in node-template (#1958)

substrate/node-template/src/cli.rs

@@ -66,6 +66,11 @@ fn run_until_exit<T, C, E>(
 
 	let _ = runtime.block_on(e.into_exit());
 	exit_send.fire();
+
+	// we eagerly drop the service so that the internal exit future is fired,
+	// but we need to keep holding a reference to the global telemetry guard
+	let _telemetry = service.telemetry();
+	drop(service);
 	Ok(())
 }