builder/amazon/*,builder/openstack: properly scrub sensitive [GH-554]
communicator/ssh: buffer file on disk to read length [GH-561]
builder/virtualbox: allow disabling guest addition uploading
website: docs on disabling guest additions
command/fix: add fixer to auto set guest_additions_mode
update CHANGELOG
command/fix: add synopsis option to fixers

This will be used in help output and such later