Fix tests updating server by name rather than id

Some tests in test_servers_negative.py update server by name rather
than id. According to the api spec[1], we should update it with id rather
name as this. PUT {tenant_id}/servers/{server_id}
[1]http://developer.openstack.org/api-ref-compute-v2.html#updateServer

Change-Id: I3b5f7831c334614e4824b99fba518a27bff3aa48
Closes-bug: #1489068
1 file changed