Do some forward porting of the old work of
mitchellh/packer's docker branch. #774
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
Rename docker post processor to docker-push.

Implement login to a docker registry, error handling
Finish up parameter parsing and validation.

Login to a docker index now works, ready for
implementation of the actual push logic.
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
Add docker-import post-processor.

Implemented initial working version
of Docker image importing code. #774
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
Merge branch 'master' of https://github.com/mitchellh/packer into docker-metadata
website: update defaults for DO ID's
Start adding dockerfile provisioning to docker-import post-processor #774
docker-import post-processor, add TODO #774
docker-import: finish up Dockerfile provisioning, Add TODO for next section #774
Implement puppet-server provisioner

This closely modeled after the same provisioner
in Vagrant.
Add docs for puppet-server provisioner
Update docs for puppet-server provisioner
Use sudo by default, as in puppet-masterless
Add missing main_test.go for puppet-server provisioner

This is required to pick up the tests with `make test`.
HTTPDownloader uses UserAgent from DownloadConfig