Pass relay parent as argument when collating (#1789)

This pr changes the collation function to also pass the current relay
parent the parachain block should be build on.

polkadot/node/overseer/src/lib.rs

@@ -1876,7 +1876,7 @@ mod tests {
 	fn test_collator_generation_msg() -> CollationGenerationMessage {
 		CollationGenerationMessage::Initialize(CollationGenerationConfig {
 			key: CollatorPair::generate().0,
-			collator: Box::new(|_| Box::new(TestCollator)),
+			collator: Box::new(|_, _| Box::new(TestCollator)),
 			para_id: Default::default(),
 		})
 	}