Stop volume leaking test_server_rescue_negative

test_server_rescue_negative created a volume, but did not deleted it.

Change-Id: Id54e34eb79547bb8197d61f91c210eba57563a03
Blueprint: stop-leaking
diff --git a/tempest/api/compute/servers/test_server_rescue_negative.py b/tempest/api/compute/servers/test_server_rescue_negative.py
index ffd79fa..4619ced 100644
--- a/tempest/api/compute/servers/test_server_rescue_negative.py
+++ b/tempest/api/compute/servers/test_server_rescue_negative.py
@@ -46,6 +46,11 @@
             cls.rescue_id, adminPass=rescue_password)
         cls.servers_client.wait_for_server_status(cls.rescue_id, 'RESCUE')
 
+    @classmethod
+    def tearDownClass(cls):
+        cls.delete_volume(cls.volume['id'])
+        super(ServerRescueNegativeTestJSON, cls).tearDownClass()
+
     def _detach(self, server_id, volume_id):
         self.servers_client.detach_volume(server_id, volume_id)
         self.volumes_extensions_client.wait_for_volume_status(volume_id,