Fix invalid filter passed to list_volumes

display_name is not a valid filter for list_volumes, i.e., for non-admin
users no matter what value we set for display_name filter, all volumes
will be returned. We'd better to use name filter for it works all the
time.
https://github.com/openstack/cinder/blob/master/doc/source/admin/generalized_filters.rst

Change-Id: Ib25f4767b74d4494edfafa211d5884a01c1b6488
diff --git a/tempest/api/volume/admin/test_volume_retype.py b/tempest/api/volume/admin/test_volume_retype.py
index 1c56eb2..9136139 100644
--- a/tempest/api/volume/admin/test_volume_retype.py
+++ b/tempest/api/volume/admin/test_volume_retype.py
@@ -36,7 +36,7 @@
         # process is finished.
         fetched_list = self.admin_volume_client.list_volumes(
             params={'all_tenants': True,
-                    'display_name': vol['name']})['volumes']
+                    'name': vol['name']})['volumes']
 
         for fetched_vol in fetched_list:
             if fetched_vol['id'] != vol['id']: