Fix testtools duplicate import

Related-Prod: PRODX-3456
Change-Id: I8a4381b2567b242d8852e4b270c057d9921b8fe8
diff --git a/barbican_tempest_plugin/tests/scenario/test_image_signing.py b/barbican_tempest_plugin/tests/scenario/test_image_signing.py
index f7db163..3badcce 100644
--- a/barbican_tempest_plugin/tests/scenario/test_image_signing.py
+++ b/barbican_tempest_plugin/tests/scenario/test_image_signing.py
@@ -15,7 +15,6 @@
 import testtools
 
 from oslo_log import log as logging
-import testtools
 
 from tempest.api.compute import base as compute_base
 from tempest.common import utils