RouterInterface delete is not robust to unavailable router

[mdbooth]

The behaviour of the RouterInterface controller is not ideal when we're waiting on the router:

• The router has not been created
• The router is currently marked unavailable

In both of these cases we don't proceed to reconcile the RouterInterface at all. At a minimum we should still iterate over RouterInterfaces and report the status as waiting on the router.

We also have a robustness issue in the case that the router is not marked as available and we are trying to delete attached RouterInterfaces. In this case, we will also never attempt to delete the RouterInterfaces. In general, I think we should attempt to delete a RouterInterface regardless of the state of its attached router, as long as the router has an ID set.