Disable vacuum page skipping in selected test cases.

By default VACUUM will skip pages that it can't immediately get
exclusive access to, which means that even activities as harmless
and unpredictable as checkpoint buffer writes might prevent a page
from being processed.  Ordinarily this is no big deal, but we have
a small number of test cases that examine the results of VACUUM's
processing and therefore will fail if the page of interest is skipped.
This seems to be the explanation for some rare buildfarm failures.
To fix, add the DISABLE_PAGE_SKIPPING option to the VACUUM commands
in tests where this could be an issue.

In passing, remove a duplicated query in pageinspect/sql/page.sql.

Back-patch as necessary (some of these cases are as old as v10).

Discussion: https://postgr.es/m/413923.1611006484@sss.pgh.pa.us

contrib/pageinspect/expected/page.out

@@ -1,7 +1,7 @@
 CREATE EXTENSION pageinspect;
 CREATE TABLE test1 (a int, b int);
 INSERT INTO test1 VALUES (16777217, 131584);
-VACUUM test1;  -- set up FSM
+VACUUM (DISABLE_PAGE_SKIPPING) test1;  -- set up FSM
 -- The page contents can vary, so just test that it can be read
 -- successfully, but don't keep the output.
 SELECT octet_length(get_raw_page('test1', 'main', 0)) AS main_0;

contrib/pageinspect/sql/page.sql

@@ -3,7 +3,7 @@ CREATE EXTENSION pageinspect;
 CREATE TABLE test1 (a int, b int);
 INSERT INTO test1 VALUES (16777217, 131584);
 
-VACUUM test1;  -- set up FSM
+VACUUM (DISABLE_PAGE_SKIPPING) test1;  -- set up FSM
 
 -- The page contents can vary, so just test that it can be read
 -- successfully, but don't keep the output.

contrib/pg_visibility/expected/pg_visibility.out

@@ -69,7 +69,7 @@ ERROR:  "test_foreign_table" is not a table, materialized view, or TOAST table
 -- check some of the allowed relkinds
 create table regular_table (a int);
 insert into regular_table values (1), (2);
-vacuum regular_table;
+vacuum (disable_page_skipping) regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
  ?column? 
 ----------
@@ -84,7 +84,7 @@ select count(*) > 0 from pg_visibility('regular_table');
 (1 row)
 
 create materialized view matview_visibility_test as select * from regular_table;
-vacuum matview_visibility_test;
+vacuum (disable_page_skipping) matview_visibility_test;
 select count(*) > 0 from pg_visibility('matview_visibility_test');
  ?column? 
 ----------
@@ -101,7 +101,7 @@ select count(*) > 0 from pg_visibility('matview_visibility_test');
 
 -- regular tables which are part of a partition *do* have visibility maps
 insert into test_partition values (1);
-vacuum test_partition;
+vacuum (disable_page_skipping) test_partition;
 select count(*) > 0 from pg_visibility('test_partition', 0);
  ?column? 
 ----------

contrib/pg_visibility/sql/pg_visibility.sql

@@ -51,13 +51,13 @@ select pg_truncate_visibility_map('test_foreign_table');
 -- check some of the allowed relkinds
 create table regular_table (a int);
 insert into regular_table values (1), (2);
-vacuum regular_table;
+vacuum (disable_page_skipping) regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
 truncate regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
 
 create materialized view matview_visibility_test as select * from regular_table;
-vacuum matview_visibility_test;
+vacuum (disable_page_skipping) matview_visibility_test;
 select count(*) > 0 from pg_visibility('matview_visibility_test');
 insert into regular_table values (1), (2);
 refresh materialized view matview_visibility_test;
@@ -65,7 +65,7 @@ select count(*) > 0 from pg_visibility('matview_visibility_test');
 
 -- regular tables which are part of a partition *do* have visibility maps
 insert into test_partition values (1);
-vacuum test_partition;
+vacuum (disable_page_skipping) test_partition;
 select count(*) > 0 from pg_visibility('test_partition', 0);
 select count(*) > 0 from pg_visibility_map('test_partition');
 select count(*) > 0 from pg_visibility_map_summary('test_partition');