Added OS field to version.Binary, version.Current

This change allows us to cache the current OS we are running on, so we will not have to do a version.GetOSFromSeries(version.Current.Series) every time we need to get the operating system type
Merge pull request #328 from gabriel-samfira/add-os-field

Added OS field to version.Binary, version.Current

This change allows us to cache the current OS we are running on, so we will not have to do a version.GetOSFromSeries(version.Current.Series) every time we need to get the operating system type