Support Bosh for RHEL/Centos based distributions

* Add RHEL/Centos support to agent
* Add cdrtools to blobs.yml and atmos blobstore
* Use powerDNS source to build the powedns - add source archive to atmos and blobs.yml
* Fix some bugs 
* Refactor bosh_agent/platform
* Add proxy support atmos_blobstore_client

Reviewers: @pmenglund