Create .git_setup_done file

The [install gitlab](https://github.com/sbadia/puppet-gitlab/blob/master/manifests/install.pp#L58) command will currently be processed every Puppet run.  In 53c1c24c when I initially refactored the module, I created the file .gitlab_setup_done, but was testing for the file .git_setup_done.  In cc27170c, @sbadia updated [setup gitlab database](https://github.com/sbadia/puppet-gitlab/blob/master/manifests/install.pp#L71) to fix the issue I had created, but overlooked [install gitlab](https://github.com/sbadia/puppet-gitlab/blob/master/manifests/install.pp#L58).  In e803258b, @sbadia added a file resource for .git_setup_done, but never created the file.  This commit addresses the creation of that file and should resolve the issue.

I am without my laptop so I will be unable to test this fix until this afternoon.