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.