Fix the logical streaming test.

Commit 7259736a6e added the capability to stream changes in ReorderBuffer
which has some tests to test the streaming mode. It is quite possible that
while this test is running a parallel transaction could be logged by
autovacuum. Such a transaction won't perform any insert/update/delete to
non-catalog tables so will be shown as an empty transaction. Fix it by
skipping the empty transactions during this test.

Per report by buildfarm.

contrib/test_decoding/expected/stream.out

@@ -26,7 +26,7 @@ TRUNCATE table stream_test;
 rollback to s1;
 INSERT INTO stream_test SELECT repeat('a', 10) || g.i FROM generate_series(1, 20) g(i);
 COMMIT;
-SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'stream-changes', '1');
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
                            data                           
 ----------------------------------------------------------
  opening a streamed block for transaction
@@ -67,7 +67,7 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (0 rows)
 
 INSERT INTO stream_test SELECT repeat('a', 6000) || g.i FROM generate_series(1, 10) g(i);
-SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'stream-changes', '1');
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
                    data                   
 ------------------------------------------
  opening a streamed block for transaction

contrib/test_decoding/sql/stream.sql

@@ -16,7 +16,7 @@ rollback to s1;
 INSERT INTO stream_test SELECT repeat('a', 10) || g.i FROM generate_series(1, 20) g(i);
 COMMIT;
 
-SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'stream-changes', '1');
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
 
 -- streaming test for toast changes
 ALTER TABLE stream_test ALTER COLUMN data set storage external;
@@ -24,7 +24,7 @@ ALTER TABLE stream_test ALTER COLUMN data set storage external;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 INSERT INTO stream_test SELECT repeat('a', 6000) || g.i FROM generate_series(1, 10) g(i);
-SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'stream-changes', '1');
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
 
 DROP TABLE stream_test;
 SELECT pg_drop_replication_slot('regression_slot');