Use immediateload for loading rules attribute
Use immediateload for loading rules attribute

With recent changes in security group rules where it uses dynamic lazy
mode for fetching security group rules, joinedload cannot be used as it is
using joined eager loading

Change-Id: I73c585a6e8d32e7556968f775011b649195ada40

stackforge/networking-arista,openstack/networking-arista,openstack/networking-arista