Document solution for wrong SSH user with Ansible

As per: https://github.com/mitchellh/vagrant/pull/2710#issuecomment-32192976
Merge pull request #3374 from follower/patch-1

Document solution for wrong SSH user with Ansible
core: ignore if box doesn't exist on update check [GH-3326]
core: outdated check checks local boxes [GH-3321]
website/docs: update docker provisioner
synced_folders/rsync: set chmod flag by default on Windows [GH-3256]
core: don't allow version for old-style box [GH-3260]
synced_folders/smb: verify PowerShell v3 is running or later [GH-3257]
TemplateRenderer can take a new root [GH-3231]
v1.5.2
website/www: up for deploy
kernel/v2: check if type is set before validation
core: Allow direct box adding again
core: BoxCollection#find version constraint can benil