Basic support for Security Groups (Basic Networking)

Hi,

I'm trying to use the vagrant-cloudstack plugin with Swiss cloud provider Exoscale (https://www.exoscale.ch/open-cloud/compute/ ) but was missing the ability to specify Security Groups (http://cloudstack.apache.org/docs/en-US/Apache_CloudStack/4.2.0/html/Installation_Guide/security-groups.html)

So I've tried adding this feature, and tested it against Exoscale's Open Cloud. It uses Basic Networking. 

However, I'm not able to test the plugin when using Advanced Networking. 

Let me know what you think...

Nicolas