AS-394: Filter incorrect groups

Adding `status` field in `scaling_groups` that will be used to filter out groups that are incorrect and are skewing our metrics. This is also the first step towards providing group status to user when the group cannot be scaled due to invalid launch configuration. 
I was stuck in `fold` thought process. This solution is much more simpler and pythonic to understand! Thank you :) I tried to do it the other.. sometimes I really don't understand why I end up thinking a more complex soln.