AS-382, AS-404: Getting load balancers in structured form

Getting load balancer nodes and time they were drained from feeds using effect.
I went with `float` since `now` [is also defined as a float](https://github.com/rackerlabs/otter/blob/master/otter/convergence.py#L275), which means that `created_at` would also need to be a float for [this to work](https://github.com/rackerlabs/otter/blob/master/otter/convergence.py#L291).  So I just assumed we were going with float for all the timestamps.

I have no particular problem with timestamps aside from ensuring that they're either all timezone aware or all timezone unaware.