Implements the proper method for terminated an auto scale group.

The current method of deleting an autoscale group is incorrect and faulty.  The current method simply deletes instances in the group, but then the group attempts to respawn them, resulting in errors such as:

```
  <Error>
    <Type>Sender</Type>
    <Code>ResourceInUse</Code>
    <Message>You cannot delete an AutoScalingGroup while there are instances or pending Spot instance request(s) still in the group.</Message>
  </Error>
  <RequestId>81ac1556-1e76-11e4-bc9b-4deda0593d7f</RequestId>
</ErrorResponse>
```

This pull request [follows Amazon's documentation](http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_DeleteAutoScalingGroup.html) for deleting AutoScale Groups:

```To remove all instances before calling DeleteAutoScalingGroup, you can call UpdateAutoScalingGroup to set the minimum and maximum size of the AutoScalingGroup to zero.```