In somes cases we need to have network without any security rules
applied, unfortunatly nova does not provide way to remove l3
assignements and always at least expose the default security group.
This commit updates code to clear security groups applied to the
network when option port_security_enabled=False is activated on the
network.
Change-Id: I630008a9733624a9d9b59b7aa3b8b2a3f8985d61
Closes-Bug: #1460630
Related-Bug: #1175464