Minor test fixes in 035_standby_logical_decoding.pl

Import usleep, which, due to an oversight in oversight in commit
48796a98d5ae was used but not imported.

Correct the comparison string used in two logfile checks. Previously, it
was incorrect and thus the test could never have failed.

Also wordsmith a comment to make it clear when hot_standby_feedback is
meant to be on during the test scenarios.

Reported-by: Melanie Plageman <[email protected]>
Author: Bertrand Drouvot <[email protected]>
Reviewed-by: Masahiko Sawada <[email protected]>
Discussion: https://postgr.es/m/flat/CAAKRu_YO2mEm%3DZWZKPjTMU%3DgW5Y83_KMi_1cr51JwavH0ctd7w%40mail.gmail.com
Backpatch-through: 16
(cherry picked from commit 74dffe5c14ac0c2e1d993968e7baa7d0cb965e8c)

Author: melanieplageman

src/test/recovery/t/035_standby_logical_decoding.pl

@@ -8,6 +8,7 @@
 
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
+use Time::HiRes qw(usleep);
 use Test::More;
 
 my ($stdin, $stdout, $stderr,
@@ -582,7 +583,7 @@ sub wait_until_vacuum_can_remove
 	  /ERROR:  cannot copy invalidated replication slot "vacuum_full_inactiveslot"/,
 	"invalidated slot cannot be copied");
 
-# Turn hot_standby_feedback back on
+# Set hot_standby_feedback to on
 change_hot_standby_feedback_and_wait_for_xmins(1, 1);
 
 ##################################################
@@ -724,12 +725,12 @@ sub wait_until_vacuum_can_remove
 
 # message should not be issued
 ok( !$node_standby->log_contains(
-		"invalidating obsolete slot \"no_conflict_inactiveslot\"", $logstart),
+		"invalidating obsolete replication slot \"no_conflict_inactiveslot\"", $logstart),
 	'inactiveslot slot invalidation is not logged with vacuum on conflict_test'
 );
 
 ok( !$node_standby->log_contains(
-		"invalidating obsolete slot \"no_conflict_activeslot\"", $logstart),
+		"invalidating obsolete replication slot \"no_conflict_activeslot\"", $logstart),
 	'activeslot slot invalidation is not logged with vacuum on conflict_test'
 );