Skip test_container_synchronization

Replace unstable_test decorator with skip due to
low pass rate of this test. The test will be unskipped
when the related bug is fixed.

Related-Bug: #1317133
Change-Id: I93613f4d89629c6dcfe72c510bced042e257695d
diff --git a/tempest/api/object_storage/test_container_sync.py b/tempest/api/object_storage/test_container_sync.py
index 6b1f849..b31ff76 100644
--- a/tempest/api/object_storage/test_container_sync.py
+++ b/tempest/api/object_storage/test_container_sync.py
@@ -126,7 +126,7 @@
                 self.assertEqual(object_content, obj_name[::-1].encode())
 
     @decorators.attr(type='slow')
-    @decorators.unstable_test(bug='1317133')
+    @decorators.skip_because(bug='1317133')
     @decorators.idempotent_id('be008325-1bba-4925-b7dd-93b58f22ce9b')
     @testtools.skipIf(
         not CONF.object_storage_feature_enabled.container_sync,