Add list servers to large ops test

Add regression test for bug 1282842, which is hit when running nova list while
waiting for instances to move to ACTIVE.

Change-Id: Ic0714834846ad94b213d97e7756ca607e1f4d710
Related-Bug: #1282842
diff --git a/tempest/scenario/test_large_ops.py b/tempest/scenario/test_large_ops.py
index b111939..91b95a8 100644
--- a/tempest/scenario/test_large_ops.py
+++ b/tempest/scenario/test_large_ops.py
@@ -47,6 +47,8 @@
 
     def _wait_for_server_status(self, status):
         for server in self.servers:
+            # Make sure nova list keeps working throughout the build process
+            self.servers_client.list_servers()
             self.servers_client.wait_for_server_status(server['id'], status)
 
     def nova_boot(self):