[AWS|ASG] filtering for ASG Scaling Activities

Allow easy filtering of ASG Scaling Activities from attributes on collection initializer. Both of these forms work:

```ruby
FogWrap.auto_scaling_api.activities("AutoScalingGroupName" => "my-asg-name")
FogWrap.auto_scaling_api.activities.all("PolicyNames" => "my-policy-name")
```

Didn't see any tests for the ASG activities for me to update :cry: