get.docker.com is now the preferred place to get Docker

Update salt configs
Handle and log errors when reading .dockercfg
Document images.
Merge pull request #1686 from jbeda/docker-site-update

get.docker.com is now the preferred place to get Docker
Document GCEPersistentDisk.
Merge pull request #1687 from erictune/fix_dockercfg

Handle and log errors when reading .dockercfg
Merge pull request #1677 from erictune/volume_docs

Document GCEPersistentDisk.
Move ObjectDiff into util
Move Codec functions to their own file
Merge pull request #1690 from erictune/image_docs

Document images.
Merge pull request #1693 from smarterclayton/move_diff

Minor moves of functions into their own files
WIP: cloud-minion