Improve the comments in 004_subscription.pl.

It was not clear whether the subscriptions in the upgraded instance were
the ones that retained the previous subscription's properties.

Author: Peter Smith
Reviewed-by: Vignesh C, Alvaro Herrera
Discussion: https://postgr.es/m/CAHut+Pu1usLPHRySPTacY1K_Q-ddSRXNFhmj_2u1NfqBC1ytng@mail.gmail.com

src/bin/pg_upgrade/t/004_subscription.pl

@@ -108,8 +108,8 @@ $old_sub->stop;
 # ------------------------------------------------------
 # Check that pg_upgrade is successful when all tables are in ready or in
 # init state (tab_upgraded1 table is in ready state and tab_upgraded2 table is
-# in init state) along with retaining the replication origin's remote lsn
-# and subscription's running status.
+# in init state) along with retaining the replication origin's remote lsn,
+# subscription's running status, and failover option.
 # ------------------------------------------------------
 command_ok(
 	[
@@ -137,15 +137,15 @@ $publisher->safe_psql(
 
 $new_sub->start;
 
-# The subscription's running status and failover option should be preserved.
-# Old subscription regress_sub1 should have enabled and failover as true while
-# old subscription regress_sub2 should have enabled and failover as false.
+# The subscription's running status and failover option should be preserved
+# in the upgraded instance. So regress_sub1 should still have subenabled and
+# subfailover set to true, while regress_sub2 should have both set to false.
 $result =
   $new_sub->safe_psql('postgres',
 	"SELECT subname, subenabled, subfailover FROM pg_subscription ORDER BY subname");
 is( $result, qq(regress_sub1|t|t
 regress_sub2|f|f),
-	"check that the subscription's running status are preserved");
+	"check that the subscription's running status and failover are preserved");
 
 my $sub_oid = $new_sub->safe_psql('postgres',
 	"SELECT oid FROM pg_subscription WHERE subname = 'regress_sub2'");