(CFACT-141) Only return major release on Windows

Windows doesn't have an official major/minor release format to its
branding (XP, Vista, 7, 8, 8.1, 10, 2008, 2008 R2, etc). We treat all
release names as the major label, and don't return a minor release label.
Kernel major/minor release are handled in a different fact.
Merge pull request #213 from MikaelSmith/task/master/CFACT-141-Windows-releases

(CFACT-141) Only return major release on Windows