Make wait_until default as 'ACTIVE' in manager.create_server

All callings to manager.create_server pass wait_until='ACTIVE',
so this is to make wail_until default as 'ACTIVE', not None.

Change-Id: I630cf047ed419fbf0cc073b5984fa29b456da451
diff --git a/tempest/scenario/test_server_multinode.py b/tempest/scenario/test_server_multinode.py
index df83063..9cc89a4 100644
--- a/tempest/scenario/test_server_multinode.py
+++ b/tempest/scenario/test_server_multinode.py
@@ -75,8 +75,7 @@
             # by getting to active state here, this means this has
             # landed on the host in question.
             inst = self.create_server(
-                availability_zone='%(zone)s:%(host_name)s' % host,
-                wait_until='ACTIVE')
+                availability_zone='%(zone)s:%(host_name)s' % host)
             server = self.servers_client.show_server(inst['id'])['server']
             servers.append(server)