Fix create server request in test_network_v6

As Nova V2.1 is much strict about API inputs, Security group name
only is accepted on create server request as a security group
parameter.

test_network_v6 passes complete security group (name, id, rules etc)
in create server request and fails for Nova V2.1.

Closes-Bug: #1414967

Change-Id: I45adde0c7c4134ea087427f23f2e45d7ec9c88e7
diff --git a/tempest/scenario/test_network_v6.py b/tempest/scenario/test_network_v6.py
index 1a82e78..dc82217 100644
--- a/tempest/scenario/test_network_v6.py
+++ b/tempest/scenario/test_network_v6.py
@@ -60,7 +60,7 @@
         self.sec_grp = self._create_security_group(tenant_id=self.tenant_id)
         self.srv_kwargs = {
             'key_name': self.keypair['name'],
-            'security_groups': [self.sec_grp]}
+            'security_groups': [{'name': self.sec_grp['name']}]}
 
     def prepare_network(self, address6_mode):
         """Creates network with