Fix condition of Swift SLO API tests run

Swift Static Large Object API tests get run even if not set slo in
[object-storage-feature-enabled] of tempest.conf.
So it always fails unless Swift's slo is enabled.

This change makes the test run only when set slo in tempest.conf.

Change-Id: I9f256e0395fd606fd1cf64d2bffd5c00802c9cf4
Closes-Bug: 1458768
diff --git a/tempest/api/object_storage/test_object_slo.py b/tempest/api/object_storage/test_object_slo.py
index 7df0dde..6fc7821 100644
--- a/tempest/api/object_storage/test_object_slo.py
+++ b/tempest/api/object_storage/test_object_slo.py
@@ -110,6 +110,7 @@
         self.assertHeaders(resp, 'Object', method)
 
     @test.idempotent_id('2c3f24a6-36e8-4711-9aa2-800ee1fc7b5b')
+    @test.requires_ext(extension='slo', service='object')
     def test_upload_manifest(self):
         # create static large object from multipart manifest
         manifest = self._create_manifest()
@@ -124,6 +125,7 @@
         self._assertHeadersSLO(resp, 'PUT')
 
     @test.idempotent_id('e69ad766-e1aa-44a2-bdd2-bf62c09c1456')
+    @test.requires_ext(extension='slo', service='object')
     def test_list_large_object_metadata(self):
         # list static large object metadata using multipart manifest
         object_name = self._create_large_object()
@@ -135,6 +137,7 @@
         self._assertHeadersSLO(resp, 'HEAD')
 
     @test.idempotent_id('49bc49bc-dd1b-4c0f-904e-d9f10b830ee8')
+    @test.requires_ext(extension='slo', service='object')
     def test_retrieve_large_object(self):
         # list static large object using multipart manifest
         object_name = self._create_large_object()
@@ -149,6 +152,7 @@
         self.assertEqual(body, sum_data)
 
     @test.idempotent_id('87b6dfa1-abe9-404d-8bf0-6c3751e6aa77')
+    @test.requires_ext(extension='slo', service='object')
     def test_delete_large_object(self):
         # delete static large object using multipart manifest
         object_name = self._create_large_object()