Improve stability of test with vacuum_truncate in reloptions.sql

This test has been using a simple VACUUM with pg_relation_size() to
check if a relation gets physically truncated or not, but forgot the
fact that some concurrent activity, like checkpoint buffer writes, could
cause some pages to be skipped.  The second test enabling
vacuum_truncate could fail, seeing a non-empty relation.  The first test
would not have failed, but could finish by testing a behavior different
than the one aimed for.  Both tests gain a FREEZE option, to make the
vacuums more aggressive and prevent page skips.

This is similar to the issues fixed in c2dc1a7.

Author: Arseny Sher
Reviewed-by: Masahiko Sawada
Discussion: https://postgr.es/m/87tuotr2hh.fsf@ars-thinkpad
backpatch-through: 12

Author: michaelpq

src/test/regress/expected/reloptions.out

@@ -102,7 +102,8 @@ SELECT reloptions FROM pg_class WHERE oid = 'reloptions_test'::regclass;
 INSERT INTO reloptions_test VALUES (1, NULL), (NULL, NULL);
 ERROR:  null value in column "i" of relation "reloptions_test" violates not-null constraint
 DETAIL:  Failing row contains (null, null).
-VACUUM reloptions_test;
+-- Do an aggressive vacuum to prevent page-skipping.
+VACUUM FREEZE reloptions_test;
 SELECT pg_relation_size('reloptions_test') > 0;
  ?column? 
 ----------
@@ -127,7 +128,8 @@ SELECT reloptions FROM pg_class WHERE oid = 'reloptions_test'::regclass;
 INSERT INTO reloptions_test VALUES (1, NULL), (NULL, NULL);
 ERROR:  null value in column "i" of relation "reloptions_test" violates not-null constraint
 DETAIL:  Failing row contains (null, null).
-VACUUM reloptions_test;
+-- Do an aggressive vacuum to prevent page-skipping.
+VACUUM FREEZE reloptions_test;
 SELECT pg_relation_size('reloptions_test') = 0;
  ?column? 
 ----------

src/test/regress/sql/reloptions.sql

@@ -61,7 +61,8 @@ CREATE TABLE reloptions_test(i INT NOT NULL, j text)
 	autovacuum_enabled=false);
 SELECT reloptions FROM pg_class WHERE oid = 'reloptions_test'::regclass;
 INSERT INTO reloptions_test VALUES (1, NULL), (NULL, NULL);
-VACUUM reloptions_test;
+-- Do an aggressive vacuum to prevent page-skipping.
+VACUUM FREEZE reloptions_test;
 SELECT pg_relation_size('reloptions_test') > 0;
 
 SELECT reloptions FROM pg_class WHERE oid =
@@ -71,7 +72,8 @@ SELECT reloptions FROM pg_class WHERE oid =
 ALTER TABLE reloptions_test RESET (vacuum_truncate);
 SELECT reloptions FROM pg_class WHERE oid = 'reloptions_test'::regclass;
 INSERT INTO reloptions_test VALUES (1, NULL), (NULL, NULL);
-VACUUM reloptions_test;
+-- Do an aggressive vacuum to prevent page-skipping.
+VACUUM FREEZE reloptions_test;
 SELECT pg_relation_size('reloptions_test') = 0;
 
 -- Test toast.* options