WiP: Add customization to Windows guests using WinRM

@clalancette,

This is a work in progress pull request to add customization to Windows guests using `WinRM`. I'm opening it for you and anyone else that want to take a look, give feedback, input, etc...

It basically relies on the module `pywinrm` (https://github.com/diyan/pywinrm) to execute the commands on the guest instance. It will offer the option of executing commands, inject files, basic package management...

Apart from the polishing & more improvements, the only issue I see now is that `pywinrm` has not official RPMs yet in the standard repositories to depend on it.

Said that, please take a look and let me know your thoughts :)