Stabilize results of brin regression test.

This test used seqscans on tenk1, with LIMIT, to build test data.
That works most of the time, but if the synchronized-seqscan logic
kicks in, we get varying test data.  This seems likely to explain
the erratic test failures on buildfarm member chipmunk, which uses
smaller-than-default shared_buffers.  To fix, add ORDER BY clauses to
force the ordering to be what it was implicitly being assumed to be.

Peter Geoghegan had noticed this with respect to one of the trouble
spots, though not the ones actually causing the chipmunk issue.

src/test/regress/expected/brin.out

@@ -55,13 +55,13 @@ INSERT INTO brintest SELECT
 	int4range(thousand, twothousand),
 	format('%s/%s%s', odd, even, tenthous)::pg_lsn,
 	box(point(odd, even), point(thousand, twothousand))
-FROM tenk1 LIMIT 100;
+FROM tenk1 ORDER BY unique2 LIMIT 100;
 -- throw in some NULL's and different values
 INSERT INTO brintest (inetcol, cidrcol, int4rangecol) SELECT
 	inet 'fe80::6e40:8ff:fea9:8c46' + tenthous,
 	cidr 'fe80::6e40:8ff:fea9:8c46' + tenthous,
 	'empty'::int4range
-FROM tenk1 LIMIT 25;
+FROM tenk1 ORDER BY thousand, tenthous LIMIT 25;
 CREATE INDEX brinidx ON brintest USING brin (
 	byteacol,
 	charcol,
@@ -238,7 +238,7 @@ INSERT INTO brintest SELECT
 	int4range(thousand, twothousand),
 	format('%s/%s%s', odd, even, tenthous)::pg_lsn,
 	box(point(odd, even), point(thousand, twothousand))
-FROM tenk1 LIMIT 5 OFFSET 5;
+FROM tenk1 ORDER BY unique2 LIMIT 5 OFFSET 5;
 VACUUM brintest;  -- force a summarization cycle in brinidx
 UPDATE brintest SET int8col = int8col * int4col;
 UPDATE brintest SET textcol = '' WHERE textcol IS NOT NULL;

src/test/regress/sql/brin.sql

@@ -56,14 +56,14 @@ INSERT INTO brintest SELECT
 	int4range(thousand, twothousand),
 	format('%s/%s%s', odd, even, tenthous)::pg_lsn,
 	box(point(odd, even), point(thousand, twothousand))
-FROM tenk1 LIMIT 100;
+FROM tenk1 ORDER BY unique2 LIMIT 100;
 
 -- throw in some NULL's and different values
 INSERT INTO brintest (inetcol, cidrcol, int4rangecol) SELECT
 	inet 'fe80::6e40:8ff:fea9:8c46' + tenthous,
 	cidr 'fe80::6e40:8ff:fea9:8c46' + tenthous,
 	'empty'::int4range
-FROM tenk1 LIMIT 25;
+FROM tenk1 ORDER BY thousand, tenthous LIMIT 25;
 
 CREATE INDEX brinidx ON brintest USING brin (
 	byteacol,
@@ -245,7 +245,7 @@ INSERT INTO brintest SELECT
 	int4range(thousand, twothousand),
 	format('%s/%s%s', odd, even, tenthous)::pg_lsn,
 	box(point(odd, even), point(thousand, twothousand))
-FROM tenk1 LIMIT 5 OFFSET 5;
+FROM tenk1 ORDER BY unique2 LIMIT 5 OFFSET 5;
 
 VACUUM brintest;  -- force a summarization cycle in brinidx