Fixed net_id key evaluation for net['id']

commit 136376f3e8b545153ac5ff6e6f918f7ef7d3d28a added the following line
net_id = net.get('uuid', net['id'])
even if net['uuid'] is present net['id'] is still evaluated and fails
since does not exist.

Change-Id: Iafa054ce300ea84a3f2439e5504d4aa768e4c4b0
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 6da0570..62ab67d 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -235,7 +235,7 @@
             # and net['id'] if they come from
             # clients.networks_client.list_networks
             for net in networks:
-                net_id = net.get('uuid', net['id'])
+                net_id = net.get('uuid', net.get('id'))
                 if 'port' not in net:
                     port = self._create_port(network_id=net_id,
                                              client=clients.ports_client,