Fix: parametrize apt::ppa class for beign able to pass options to apt-add-repository command

Hi!

Using the puppetlabs-apt module on our platform we've noticed that even if we manualy added repositories keys before adding a launchpad repo using `apt::ppa` class, the operation would fail because `apt-add-repository` would ask for user input.

We've fixed the `apt::ppa` class to support a `options` parameter allowing to pass options to the underlying `apt-add-repository` execution. As a default 'options' is set to '-y' to avoid user prompt. We found it might be usefull to anyone so here's our pull request.

Thanks