Migrate volume API tests to resource_* fixtures

Partially-implements bp resource-cleanup

Change-Id: Ib92d30d25592c38a5999d43e533921377200570f
diff --git a/tempest/api/volume/admin/test_volumes_backup.py b/tempest/api/volume/admin/test_volumes_backup.py
index 3699e9c..8b90b07 100644
--- a/tempest/api/volume/admin/test_volumes_backup.py
+++ b/tempest/api/volume/admin/test_volumes_backup.py
@@ -27,9 +27,8 @@
     _interface = "json"
 
     @classmethod
-    @test.safe_setup
-    def setUpClass(cls):
-        super(VolumesBackupsTest, cls).setUpClass()
+    def resource_setup(cls):
+        super(VolumesBackupsTest, cls).resource_setup()
 
         if not CONF.volume_feature_enabled.backup:
             raise cls.skipException("Cinder backup feature disabled")