Autoscaling Support

Feedback requested/appreciated.

Adds support for EC2 autoscaling groups as a new cluster type.I followed the example set by the RDS provider. It doesn't exactly mash with how Ironfan looks at the world but might be good enough to be usable.

Known issues:
* Each AS group gets a pointless Chef node. I haven't been able to figure out a good way to indicate that nodes are irrelevant for a particular provider.
* Cluster show doesn't give useful output for paused AS groups.
* Cluster stop pauses the AS group without killing its instances. This breaks with convention but was determined to be more in line with what our operations folks really wanted. Could be made more conventional with the addition of new cluster pause/unpause actions that only apply to AS groups.
* It is anticipated that the desired size will be controlled by operations and not in cluster definitions, beyond initial launch.
* Several autoscaling attributes have not yet been fully implemented. (VPC, Termination policy, etc)
* Tags have not yet been applied.
* Tests :-\

There are likely more problems that haven't been fully exposed yet but this should be enough for a conversation about mergeability.

cc/@gerbercj