Expose final paths

Move some path logic into resource to expose final paths. Useful for doing things like this in other recipes:

```rb
cert1 = certificate_manage 'example.com'
where_did_it_go1 = File.join cert1.cert_path, cert1.certificate # => /etc/ssl/certs/example.com.pem

cert2 = certificate_manage 'example.com' do
  cert_path '/bobs/emporium'
  create_subfolders false
end
where_did_it_go2 = File.join cert2.cert_path, cert2.certificate # => /bobs/emporium/example.com.pem
```