Make PG checkpoint test less flaky

Only run checkpoint and check metrics on the primary. This will remove
the possible uncertainty of having the Checkpoint record being correctly
propagated to the standby before standby's checkpoint is triggered.

Author: bonnefoa

postgres/tests/test_pg_replication.py

@@ -221,22 +221,18 @@ def test_conflicts_bufferpin(aggregator, integration_check, pg_instance, pg_repl
 
 
 @requires_over_10
-def test_pg_control_replication(aggregator, integration_check, pg_instance, pg_replica_instance):
-    check = integration_check(pg_replica_instance)
+def test_pg_control_replication(aggregator, integration_check, pg_instance):
+    check = integration_check(pg_instance)
     check.run()
 
-    dd_agent_tags = _get_expected_tags(check, pg_replica_instance, role='standby')
+    dd_agent_tags = _get_expected_tags(check, pg_instance, role='master')
     aggregator.assert_metric('postgresql.control.timeline_id', count=1, value=1, tags=dd_agent_tags)
 
     # Also checkpoint on primary to generate changes
     master_conn = _get_superconn(pg_instance)
     with master_conn.cursor() as cur:
         cur.execute("CHECKPOINT;")
 
-    postgres_conn = _get_superconn(pg_replica_instance)
-    with postgres_conn.cursor() as cur:
-        cur.execute("CHECKPOINT;")
-
     aggregator.reset()
     check.run()
     # checkpoint should be less than 2s old