Remove test_create_server_response

If enable_instance_password is set to False in nova.conf, the response
of "create a server" API does not contain AdminPass/admin_password.
In addition, the response already is checked with JSON schema definition.
So test_create_server_response became unnecessary.

Change-Id: Id62a8d447c36eaf0b1f64a93929c4cfa2c20e2ae
Merge "Remove test_create_server_response"