Add Rackspace Autoscale modules

- rax_scaling_group
- rax_scaling_policy
Back-porting 1.6.x release info into CHANGELOG/RELEASES and packaging
Merge branch 'rax-autoscale' of https://github.com/sivel/ansible into sivel-rax-autoscale
Adding new rax_scaling* modules to the CHANGELOG
Merge branch 'sivel-rax-autoscale' into devel