Allow changing ingress rules after security group creation

* Updated the acceptance test to check both that rules are added
* and that rules are deleted
We could also verify AWS is stable for certain by doing a little test that adds security groups `a` through `z` in some random order, adds them in a random order to security group `a`, and then verifies how AWS returns them in `ip_permissions`.

I think we'll see that they always come back ordered.  Given 26 possible options, a few runs through that should be enough to trigger an out of order response from AWS if it really isn't providing a stable sort.  I would suspect though that we see them always come back in order.