Add a $destination_dir param

[LinguineCode]

It would be cool if I could do this. I should be able to send a PR.

 $rhsm_sslcerts = hiera(rhsm::register::sslcerts)

  wget::fetch { $rhsm_sslcerts:
    destination_dir => '/etc/rhsm/ca/',
  }

hiera:

---
rhsm::register::sslcerts:
 - 'http://mysatelliteserver.mycompany.com/pub/certs/mycert-local.pem':
 - 'http://mysatelliteserver.mycompany.com/pub/certs/another-file-ca.pem':

And it downloads the files to /<destination_dir>/<filename cut from url>

[carlossg]

see #58