WIP: Re-implement WMI support, remove a dependency

This change removes the dependency on ruby-wmi-rdp, though re-factoring is needed.

The WmiRepository class should probably be more of a utility class with no instance methods.

Additionally, a copy of the WmiRepository class exists in Chef -- they should probably share a common gem, or Ohai should expose the class so Chef can use it. @danielsdeleo, thoughts on these options?