satellite/gracefulexit: use placement when gracefulexit pick new nodes

It's quite straightforward change, and AFAIK graceful exit will be decommissioned very soon.

Therefore I didn't create big unit tests, yet. But I can be convinced to invest more time.

Change-Id: Ia588e516d7af5171fa47f9bab100edd3bf2b2cf9

satellite/gracefulexit/endpoint.go

@@ -404,6 +404,7 @@ func (endpoint *Endpoint) processIncomplete(ctx context.Context, stream pb.DRPCS
 	request := &overlay.FindStorageNodesRequest{
 		RequestedCount: 1,
 		ExcludedIDs:    excludedIDs,
+		Placement:      segment.Placement,
 	}
 
 	newNodes, err := endpoint.overlay.FindStorageNodesForGracefulExit(ctx, *request)