website/docs: link to real vagrant cloud url

This is mostly for cookies and google. If you're logged in to
www, you won't be logged in to apex, and visa versa. Also a Vagrant
Cloud bug but wanted to make it consistent on this end.
Merge pull request #3189 from mitchellh/docs-www-vagrant-cloud

website/docs: link to real vagrant cloud url
kernel/v2: validate forwarded ports [GH-3187]
core: Downloads with user/pass use curl -u flag [GH-3183]
core: vagrant help no longer loads Vagrantfile
guests/linux: rsync only chown if invalid user/group [GH-3186]
guests/linux: check for proper owner [GH-3186]
guests/linux: one more time
v1.5.1
website/www: update for deploy
Up version for dev
Set the Bundler UI only if we enable it [GH-3193]
Update CHANGELOG