Refactor Puppet bits for the nightly builds NFS

Now that we introduced the tails::jenkins::artifacts_store class, we should also abstract in there the NFS part of nightly.t.b.o.

That will also be the moment where to put more logic in this class, like dealing with the File[$artifacts_store_path] questions.

Parent Task: #9614

Original created by @bertagaz on 9616 (Redmine)

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