cleanup for dreambox_openpli_shell

Hi @m-1-k-3 ,

This pull request is related to https://github.com/rapid7/metasploit-framework/pull/1496

I've done the final module cleanup for myself, please feel free to review changes, ask any doubt about my changes and once you can verify it's working it will be ready to merge. Just land it on your repo and the original PR will be updated.

I've verified the generated http request and it seems okay, but since I've not a real device to test, I'll need your help again!