Don't try to cleanup volume that doesn't exist.

Updates the test_volume_create_get_delete test so that it no
longer tries to cleanup when the volume variable is None.

This resolves UnboundLocalError errors which can occur in
the test suite when volumes aren't getting created correctly.

Change-Id: I483219c4bb78c9dbc21be7a974bd208014ec1740
diff --git a/tempest/tests/compute/volumes/test_volumes_get.py b/tempest/tests/compute/volumes/test_volumes_get.py
index e80e5b9..0a207b9 100644
--- a/tempest/tests/compute/volumes/test_volumes_get.py
+++ b/tempest/tests/compute/volumes/test_volumes_get.py
@@ -26,6 +26,7 @@
     @attr(type='smoke')
     def test_volume_create_get_delete(self):
         """CREATE, GET, DELETE Volume"""
+        volume = None
         try:
             v_name = rand_name('Volume-%s-') % self._interface
             metadata = {'Type': 'work'}
@@ -61,11 +62,12 @@
                              'from the created Volume')
 
         finally:
-            #Delete the Volume created in this method
-            resp, _ = self.client.delete_volume(volume['id'])
-            self.assertEqual(202, resp.status)
-            #Checking if the deleted Volume still exists
-            self.client.wait_for_resource_deletion(volume['id'])
+            if volume:
+                #Delete the Volume created in this method
+                resp, _ = self.client.delete_volume(volume['id'])
+                self.assertEqual(202, resp.status)
+                #Checking if the deleted Volume still exists
+                self.client.wait_for_resource_deletion(volume['id'])
 
     @attr(type='positive')
     def test_volume_get_metadata_none(self):