Fix for issue 4806

Added ability to detect errors printed to stderr in the WinRM communicator, and an options flag to fail tests if the stderr has values in it.

This is needed because the check for ubuntu when provided to the WinRM communicator doesn't set an exit code, it does however print information to stderr. As no exit code is set, Vagrant assumes that the box is running ubuntu, which then fails all subsequent steps (e.g. shared folders).

https://github.com/mitchellh/vagrant/issues/4806