add OS::Heat::AutoScalingGroup

Adds a new resource for scaling arbitrary resources. Similar
to the way ResourceGroup works, but mixed with AutoScalingGroup.

Rolling updates will be supported in a forthcoming patch.

Change-Id: I4212de46bb15f91e35088724970510cb0594d303
Implements: partial blueprint as-intermediate-resources
Merge "add OS::Heat::AutoScalingGroup"