Remove nova v2 client in ListSnapshotImagesTest

ListSnapshotImagesTest should only use nova v3 client for creating
snapshot as the similar test which uses nova v2 client already exist
in nova v2 images api tests(compute/images/test_list_image_filters.py).
This patch removes nova v2 client from ListSnapshotImagesTest.

Change-Id: I04e34f7cd34f760d7bc1361a3037c1f1fe1341d8
Closes-Bug: #1311712
diff --git a/tempest/api/image/v1/test_images.py b/tempest/api/image/v1/test_images.py
index b90891b..96729ee 100644
--- a/tempest/api/image/v1/test_images.py
+++ b/tempest/api/image/v1/test_images.py
@@ -247,11 +247,17 @@
     @classmethod
     @test.safe_setup
     def setUpClass(cls):
-        super(ListSnapshotImagesTest, cls).setUpClass()
+        # This test class only uses nova v3 api to create snapshot
+        # as the similar test which uses nova v2 api already exists
+        # in nova v2 compute images api tests.
+        # Since nova v3 doesn't have images api proxy, this test
+        # class was added in the image api tests.
         if not CONF.compute_feature_enabled.api_v3:
-            cls.servers_client = cls.os.servers_client
-        else:
-            cls.servers_client = cls.os.servers_v3_client
+            skip_msg = ("%s skipped as nova v3 api is not available" %
+                        cls.__name__)
+            raise cls.skipException(skip_msg)
+        super(ListSnapshotImagesTest, cls).setUpClass()
+        cls.servers_client = cls.os.servers_v3_client
         cls.servers = []
         # We add a few images here to test the listing functionality of
         # the images API
@@ -281,8 +287,7 @@
         cls.servers.append(server)
         cls.servers_client.wait_for_server_status(
             server['id'], 'ACTIVE')
-        resp, image = cls.servers_client.create_image(
-            server['id'], name)
+        resp, _ = cls.servers_client.create_image(server['id'], name)
         image_id = data_utils.parse_image_id(resp['location'])
         cls.created_images.append(image_id)
         cls.client.wait_for_image_status(image_id,