Remove unnecessary secgroup attrs from scenario tests

Nova "create a server" API refers a security group name only in
security group attributes, but current scenario tests pass the
other attributes(rules, tenant_id, description) also.
That will be a problem on Nova v2.1 API because the API denies
unnecessary attributes for strict validation.
This patch removes them.

Change-Id: I764f00fc1e6a5486367a95a44976e41293aa84c0
diff --git a/tempest/scenario/test_large_ops.py b/tempest/scenario/test_large_ops.py
index 91b95a8..83b5aff 100644
--- a/tempest/scenario/test_large_ops.py
+++ b/tempest/scenario/test_large_ops.py
@@ -60,7 +60,7 @@
             self.image,
             flavor_id,
             min_count=CONF.scenario.large_ops_number,
-            security_groups=[secgroup])
+            security_groups=[{'name': secgroup['name']}])
         # needed because of bug 1199788
         params = {'name': name}
         _, server_list = self.servers_client.list_servers(params)