I don't think that it makes sense to pass in a package attribute to the raid provider.  The provider should either support the `filesystem` or not.

For this feature, the only package that is required to support formatting an xfs filesystem is `xfsprogs`.  The others add functionality not specific to the provider.  When adding xfs in my local fork, I inserted the following before the `ruby_block "formatting md device..."` that performs the format actions:

```ruby    
if filesystem == "xfs"
  package "xfsprogs" do
    action :install
  end
end
```

I'm not in love with it living outside the format/filesystem logic, but I didn't want to refactor out the `ruby_block` to allow a `package` call.