Run git from tmp working directory

I have a puppet module that uses this one. It's often applied interactively (puppet apply x.pp) -- but git::repo fails because git clone tries to cd *back* as $user to the starting point (/root).

    Jul 11 19:21:03 fedora.katello.example.org puppet-agent[12354]: (/Stage[main]/Stbenjam
    ::Git/Git::Repo[vundle]/Exec[git_repo_for_vundle]/returns) fatal: Could not change back
    to '/root': Permission denied

Since we dropped puppet 2.6 we can use trailing commas.