Fixed current_resource.name assignment in providers.

While investigating another issue, I found out that the load_current_resource methods all providers initialize the current_resource with the new_resource instance. This is incorrect (even if this does not stop the resources from converging) but it makes inspecting the current_resource more difficult to read (the name attribute will be an object instead of the expected string).

In the example given in the [official documentation](http://docs.getchef.com/lwrp_custom_provider.html#load-current-resource) the current_resource is instantiated using the new_resource name attribute, which is exactly what this PR does.