[AWS|ASG] filtering for ASG Scaling Policies

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