Choose a security group when creating an instance with a port that has disabled port security

[sunhao]

Description
===========
When creating an instance using a port that has disabled port security, if you choose a security group, an error should be expected to throw an exception, but the result is that the creation is successful. Although the instance as expected no security group, but I think in the process of creating an instance should throw an exception and give some hints, instead of successfully creating but not displaying the security group.

Steps to reproduce
==================
* Create an instance use a port that has disabled port security
* Use the port in the previous step to create an instance, and select a security group when creating the instance.

Expected result
===============
Instance creation failed and an exception was thrown.

Actual result
=============
Successfully created instance

[Stephen Finucane (stephenfinucane)]

This is expected behavior. From the API reference:

  One or more security groups. Specify the name of the security group in the name attribute. If you
  omit this attribute, the API creates the server in the default security group. Requested security
  groups are not applied to pre-existing ports.

This is a pre-existing port so the security groups will not apply.

[1] https://docs.openstack.org/api-ref/compute/?expanded=create-server-detail#id11