provisioners: Import Docker provisioner code from Vocker
provisioners/docker: Simplify raising of Docker related errors
provisioner/docker: Add missing I18n
provisioners/docker: Clean up some leftovers from vocker
Add cleanup routine to synced folder plugin implementation
provisioners/docker: make sure version is correct type, fix Ruby warning
provisioners/docker: style nitpick on unless
provisioners/docker: allow images to be configured with images:
provisioners/docker: simplify run, output which are running
provisioners/docker: only allow 'args' special
provisioners/docker: style nitpicks
provisioners/docker: output for each image pulling
provisioners/docker: output version when installing
core: Set I18n.config.enforce_available_locales to true to avoid an annoying deprecation warning
provisioners/docker: use proper UNSET_VALUE for no value
website/docs: document the Docker provisioner
Merge pull request #2549 from mitchellh/f-docker-provisioner

docker provisioner
Update CHANGELOG
Merge pull request #2575 from fgrehm/remove-18n-deprecation-warning

Set I18n.config.enforce_available_locales to true to avoid an annoying deprecation warning
Merge pull request #2561 from emyl/synced-folder-cleanup-v2

core: Enhance the synced folder plugin implementation with a cleanup routine