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Minor fixes and improvements to the Vagrantfile
Well, this script is *not* supposed to manipulate the local system, especially not the file-system and definitely not `/etc` (because it should never be executed as `root` anyway..).
Thus, without having a more recent version of `puppet(8)` available, we have to ensure the canonical paths are set up properly *before* this script is executed - which is why these operations are better placed in `install-precise.rb`.