Optimize case when we don't have permanent logical slots (#2121)

The unnecessary call of SlotsHandler.process_permanent_slots() results in one additional query to `pg_replication_slots` view every HA loop.

features/patroni_api.feature

@@ -71,6 +71,7 @@ Scenario: check API requests for the primary-replica pair in the pause mode
 	When I run patronictl.py restart batman postgres1 --force
 	Then I receive a response returncode 0
 	Then replication works from postgres0 to postgres1 after 20 seconds
+	And I sleep for 2 seconds
 	When I issue a GET request to http://127.0.0.1:8009/replica
 	Then I receive a response code 200
 	And I receive a response state running

patroni/postgresql/__init__.py

@@ -327,6 +327,9 @@ class Postgresql(object):
         if cluster and cluster.config and cluster.config.modify_index:
             self._has_permanent_logical_slots =\
                 cluster.has_permanent_logical_slots(self.name, nofailover, self.major_version)
+
+            # We want to enable hot_standby_feedback if the replica is supposed
+            # to have a logical slot or in case if it is the cascading replica.
             self.set_enforce_hot_standby_feedback(
                 self._has_permanent_logical_slots or
                 cluster.should_enforce_hot_standby_feedback(self.name, nofailover, self.major_version))
@@ -338,7 +341,9 @@ class Postgresql(object):
                 cluster_info_state = dict(zip(['timeline', 'wal_position', 'replayed_location',
                                                'received_location', 'replay_paused', 'pg_control_timeline',
                                                'received_tli', 'slot_name', 'conninfo', 'slots'], result))
-                cluster_info_state['slots'] = self.slots_handler.process_permanent_slots(cluster_info_state['slots'])
+                if self._has_permanent_logical_slots:
+                    cluster_info_state['slots'] =\
+                        self.slots_handler.process_permanent_slots(cluster_info_state['slots'])
                 self._cluster_info_state = cluster_info_state
             except RetryFailedError as e:  # SELECT failed two times
                 self._cluster_info_state = {'error': str(e)}