delete servers in setUpClass if ecxeption raised

this catch the exception in setUpClass of test_images_oneserver
and delete the server. Every exception should be catched
so hasn't specify what kind of exception after except.

fix bug 1158843

Change-Id: I4ea4f6b4bc97a514393c0d0cb6236dcc720fd1a0
diff --git a/tempest/tests/compute/images/test_images_oneserver.py b/tempest/tests/compute/images/test_images_oneserver.py
index 9412d39..ca3dbb5 100644
--- a/tempest/tests/compute/images/test_images_oneserver.py
+++ b/tempest/tests/compute/images/test_images_oneserver.py
@@ -41,7 +41,12 @@
         super(ImagesOneServerTestJSON, cls).setUpClass()
         cls.client = cls.images_client
         cls.servers_client = cls.servers_client
-        resp, cls.server = cls.create_server(wait_until='ACTIVE')
+
+        try:
+            resp, cls.server = cls.create_server(wait_until='ACTIVE')
+        except Exception:
+            cls.tearDownClass()
+            raise
 
         cls.image_ids = []