Fixed issue 3918

Running Windows guest commands through a scheduled task were not returning the correct exit codes, they were only returning 1 or 0. This has negative consequences especially for Puppet which can return an exit code of 2 for partial success.

Since we're running an executable from inside a powershell encoded command we need to ensure we explicitly propagate the exit code to the original caller just like a regular PowerShell script - in this case cmd /c which in return is called from a scheduled task.
Merge pull request #3922 from mitchellh/fix-issue-3918

communicator/winrm: proper exit code for powershell
Update CHANGELOG.md
Fixed minor typo.
Fixed minor typos.
Remove references to slave

Instead of calling things slaves, either rename them to "nodes" or "followers",
depending on the context
Update the Vagrantfiles included in website

use 'hashicorp/precise64', otherwise I get errors on initial `vagrant up`
Merge pull request #3930 from catsby/remove_slave

website: Remove references to slave
Merge pull request #3927 from rockymadden/master

Fixed minor typos.
Merge pull request #3926 from rockymadden/master

Fixed minor typo.
Merge pull request #3933 from catsby/update_website_vagrantfiles

Update the Vagrantfiles included in website
v1.6.3
website/www: up version
Up version for dev
Fix typo in multi-machine doc
Merge pull request #3946 from thierrymarianne/typo-fix-in-multiple-machine-doc

website/docs: Fix typo in multi-machine doc