DisablePortSecurity implementation causes incompatitibily issues

[qvicksilver]

/kind bug

What steps did you take and what happened:
I'm trying to provision Kubernetes Cluster on Top of our OpenStack platform, which does not have the port security extension enabled. However the provider fails to provision the network due to the missing extension.

E0611 08:10:18.281288       1 controller.go:258] controller-runtime/controller "msg"="Reconciler error" "error"="failed to reconcile network: Bad request with: [POST https://<redacted>:9696/v2.0/networks], error message: {\"NeutronError\": {\"message\": \"Unrecognized attribute(s) 'port_security_enabled'\", \"type\": \"HTTPBadRequest\", \"detail\": \"\"}}"  "controller"="openstackcluster" "request"={"Namespace":"default","Name":"capi-quickstart"}

What did you expect to happen:
Successfully provisioning a working Kubernetes cluster running on our OpenStack platform.

Anything else you would like to add:
We currently run Kubernetes clusters on top of our OpenStack platform using Calico IP in IP encapsulation without the port security extension. Forcing the use of an OpenStack extension that is not required for operation seems odd imho.
Simply commenting the code that forces the extension to be included results in a working cluster. This issue seems to fall in the same category as #543.

Environment:

• Cluster-api version: v0.3.6-90-7b9762100a1d48-dirty
• Minikube/KIND version: v0.9.0-alpha+b3e81f69654a36
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):