Add ability to skip for test_signed_image_upload_boot_snapshot

when environment doesn't have an ability to sing image,
this test will fail, for this case
added test skip condition.

Change-Id: I426e0eb9e94386578d5ee2e756edd128a2dd9f0a
Related-prod: PRODX-5292
(cherry picked from commit c272618c8bcca3172aedfe38205e88e563ffeb90)
(cherry picked from commit 5d3034bf89b2ce1f9f54fd2208c9c45beb744471)
(cherry picked from commit 5d22bfa1d264a353fcbae884bbcf7a403775e8b5)
diff --git a/barbican_tempest_plugin/tests/scenario/test_image_signing.py b/barbican_tempest_plugin/tests/scenario/test_image_signing.py
index 3e8cf05..19d2a1f 100644
--- a/barbican_tempest_plugin/tests/scenario/test_image_signing.py
+++ b/barbican_tempest_plugin/tests/scenario/test_image_signing.py
@@ -106,6 +106,9 @@
 
     @decorators.idempotent_id('f0603dfd-8b2c-44e2-8b0f-d65c87aab257')
     @utils.services('compute', 'image')
+    @testtools.skipUnless(
+        CONF.compute_feature_enabled.barbican_integration_enabled,
+        'Barbican integration must be enabled.')
     def test_signed_image_upload_boot_snapshot(self):
         """Test that Glance can snapshot an instance using a signed image.