No superuser check separated from other tests

The output differs across versions because it can include the context.

This made:

- repack.out = repack_1.out
- repack_3.out = repack_5.out

regress/expected/nosuper_1.out

@@ -0,0 +1,17 @@
+--
+-- no superuser check
+--
+SET client_min_messages = error;
+DROP ROLE IF EXISTS nosuper;
+SET client_min_messages = warning;
+CREATE ROLE nosuper WITH LOGIN;
+-- => OK
+\! pg_repack --dbname=contrib_regression --table=tbl_cluster --no-superuser-check
+INFO: repacking table "tbl_cluster"
+-- => ERROR
+\! pg_repack --dbname=contrib_regression --table=tbl_cluster --username=nosuper
+ERROR: pg_repack failed with error: You must be a superuser to use pg_repack
+-- => ERROR
+\! pg_repack --dbname=contrib_regression --table=tbl_cluster --username=nosuper --no-superuser-check
+ERROR: pg_repack failed with error: ERROR:  permission denied for schema repack
+DROP ROLE IF EXISTS nosuper;