DO NOT MERGE.  spike a fixup for windows

Call .instances so that @provider.package gets populated, and uninstall can be
called.

https://github.com/puppetlabs/puppet/blob/3.4.2/lib/puppet/provider/package/windows.rb#L30-L36
https://github.com/puppetlabs/puppet/blob/3.4.2/lib/puppet/provider/package/windows.rb#L66-L71