Two-stage upgrade for parachains (#392)

* Authorised upgrade doesn't pay fee

* Origin not needed

* Fixes

pallets/parachain-system/src/lib.rs

@@ -258,14 +258,15 @@ decl_module! {
 		}
 
 		#[weight = 1_000_000]
-		fn enact_authorized_upgrade(origin, code: Vec<u8>) {
+		fn enact_authorized_upgrade(_origin, code: Vec<u8>) -> DispatchResultWithPostInfo {
 			// No ensure origin on purpose. We validate by checking the code vs hash in storage.
 			let required_hash = AuthorizedUpgrade::<T>::get()
 				.ok_or(Error::<T>::NothingAuthorized)?;
 			let actual_hash = T::Hashing::hash(&code[..]);
 			ensure!(actual_hash == required_hash, Error::<T>::Unauthorized);
 			Self::set_code_impl(code)?;
 			AuthorizedUpgrade::<T>::kill();
+			Ok(Pays::No.into())
 		}
 
 		fn on_finalize() {