Change SpawnedSubsystem type to log subsystem errors (#1878)

* Change SpawnedSubsystem type to log subsystem errors

* Remove clone

polkadot/node/subsystem/src/lib.rs

@@ -164,7 +164,7 @@ pub struct SpawnedSubsystem {
 	/// Name of the subsystem being spawned.
 	pub name: &'static str,
 	/// The task of the subsystem being spawned.
-	pub future: BoxFuture<'static, ()>,
+	pub future: BoxFuture<'static, SubsystemResult<()>>,
 }
 
 /// A `Result` type that wraps [`SubsystemError`].
@@ -233,8 +233,8 @@ impl<C: SubsystemContext> Subsystem<C> for DummySubsystem {
 		let future = Box::pin(async move {
 			loop {
 				match ctx.recv().await {
-					Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => return,
-					Err(_) => return,
+					Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => return Ok(()),
+					Err(_) => return Ok(()),
 					_ => continue,
 				}
 			}