Correctly call client inits from test_multi_backend

This commit fixes the client init calls in setUpClass for
test_mult_backend. Since this doesn't run in the gate it slipped through
the massive config refactor.

Closes-Bug: #1276215

Change-Id: Ibcd521a5b5c3f4d755387b29ee73dcc042c44fa0
diff --git a/tempest/api/volume/admin/test_multi_backend.py b/tempest/api/volume/admin/test_multi_backend.py
index 96e0264..cb1a6cb 100644
--- a/tempest/api/volume/admin/test_multi_backend.py
+++ b/tempest/api/volume/admin/test_multi_backend.py
@@ -41,13 +41,11 @@
         adm_tenant = CONF.identity.admin_tenant_name
         auth_url = CONF.identity.uri
 
-        cls.volume_client = volumes_client.VolumesClientJSON(CONF,
-                                                             adm_user,
+        cls.volume_client = volumes_client.VolumesClientJSON(adm_user,
                                                              adm_pass,
                                                              auth_url,
                                                              adm_tenant)
-        cls.type_client = volume_types_client.VolumeTypesClientJSON(CONF,
-                                                                    adm_user,
+        cls.type_client = volume_types_client.VolumeTypesClientJSON(adm_user,
                                                                     adm_pass,
                                                                     auth_url,
                                                                     adm_tenant)