Fixing tests for DQA with ROLLUP()

Post window function Postgres merge, queries with distinct qualified
aggs and ROLLUP were generating wrong results. This issue fixed by
disabling the guc gp_enable_groupext_distinct_pruning
Signed-off-by: NHaisheng Yuan <hyuan@pivotal.io>

src/backend/utils/misc/guc_gp.c

@@ -904,7 +904,7 @@ struct config_bool ConfigureNamesBool_gp[] =
 			NULL,
 		},
 		&gp_enable_groupext_distinct_pruning,
-		true, NULL, NULL
+		false /* GPDB_84_MERGE_FIXME: Turn GUC back to true and fix the failing tests */, NULL, NULL
 	},
 
 	{