Skip integration tests when Swift is not available

Let's skip integration tests using Swift when the service is not
available. It will help turn the py3 gate green.

Change-Id: Ib3536583dbb3bbf50d9c64976e909fd352391d05
diff --git a/functional/test_swiftsignal_update.py b/functional/test_swiftsignal_update.py
index 0cf2f81..9e656b1 100644
--- a/functional/test_swiftsignal_update.py
+++ b/functional/test_swiftsignal_update.py
@@ -34,6 +34,8 @@
 class SwiftSignalHandleUpdateTest(functional_base.FunctionalTestsBase):
 
     def test_stack_update_same_template_replace_no_url(self):
+        if not self.is_service_available('object-store'):
+            self.skipTest('object-store service not available, skipping')
         stack_identifier = self.stack_create(template=test_template)
         stack = self.client.stacks.get(stack_identifier)
         orig_url = self._stack_output(stack, 'signal_url')