Change keypair client to return one value and update tests

Partially implements: blueprint clients-return-one-value

Change-Id: Ief3c882164917062f1874182ba9ab1732f347d0d
diff --git a/tempest/stress/cleanup.py b/tempest/stress/cleanup.py
index b494db6..b34ea56 100644
--- a/tempest/stress/cleanup.py
+++ b/tempest/stress/cleanup.py
@@ -37,7 +37,7 @@
         except Exception:
             pass
 
-    _, keypairs = admin_manager.keypairs_client.list_keypairs()
+    keypairs = admin_manager.keypairs_client.list_keypairs()
     LOG.info("Cleanup::remove %s keypairs" % len(keypairs))
     for k in keypairs:
         try: