Fix test instability

On FreeBSD, the new test fails due to a WAL file being removed before
the standby has had the chance to copy it.  Fix by adding a replication
slot to prevent the removal until after the standby has connected.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reported-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/CAEze2Wj5nau_qpjbwihvmXLfkAWOZ5TKdbnqOc6nKSiRJEoPyQ@mail.gmail.com

Author: alvherre

src/test/recovery/t/033_replay_tsp_drops.pl

@@ -24,6 +24,7 @@ sub test_tablespace
 			CREATE TABLESPACE source_ts  LOCATION '';
 			CREATE TABLESPACE target_ts  LOCATION '';
 			CREATE DATABASE template_db IS_TEMPLATE = true;
+			SELECT pg_create_physical_replication_slot('slot', true);
 		]);
 	my $backup_name = 'my_backup';
 	$node_primary->backup($backup_name);
@@ -38,10 +39,11 @@ sub test_tablespace
 	# Make sure connection is made
 	$node_primary->poll_query_until('postgres',
 		'SELECT count(*) = 1 FROM pg_stat_replication');
+	$node_primary->safe_psql('postgres', "SELECT pg_drop_replication_slot('slot')");
 
 	$node_standby->safe_psql('postgres', 'CHECKPOINT');
 
-	# Do immediate shutdown just after a sequence of CREAT DATABASE / DROP
+	# Do immediate shutdown just after a sequence of CREATE DATABASE / DROP
 	# DATABASE / DROP TABLESPACE. This causes CREATE DATABASE WAL records
 	# to be applied to already-removed directories.
 	my $query = q[