Package install fix for not honoring exit codes

The exit code was not being honored from the package provider.  It was exiting with success on failure.

If we ran a recipe like the following: https://github.com/Webtrends/ms_dotnet4/blob/master/recipes/default.rb

It would succeed on the windows_package command, even though .NET was not being installed.  We were using winrm at the time to run chef-client and this will make .NET 4 install always fail.  So we were able to constantly reproduce the exit code issue.  The current commit fixed this for us and I assume would also help others with false exit codes.
Yes - This wasn't being used so I thought I would delete it to make it clearer to understand. Technically I thought the right way to do this was to actually start using it since we use it for install. However, I thought that would introduce more regressions.

Figured this is being eventually integrated into core chef, and I just wanted the code here to be as correct as possible, and worry about method design as part of the integration process that has already started with the MSI based code.