query executor: better handling of errors for host selection

We cannot mark the host as failed in case of logical errors, whether it is from
gocql itself or from the context package.

query_executor.go

@@ -112,7 +112,15 @@ func (q *queryExecutor) do(ctx context.Context, qry ExecutableQuery) *Iter {
 		iter = q.attemptQuery(ctx, qry, conn)
 		iter.host = selectedHost.Info()
 		// Update host
-		selectedHost.Mark(iter.err)
+		switch iter.err {
+		case context.Canceled, context.DeadlineExceeded, ErrNotFound:
+			// those errors represents logical errors, they should not count
+			// toward removing a node from the pool
+			selectedHost.Mark(nil)
+			return iter
+		default:
+			selectedHost.Mark(iter.err)
+		}
 
 		// Exit if the query was successful
 		// or no retry policy defined or retry attempts were reached