Running Puppet manually (not using a daemon, eg. puppet agent -t) will run the Brew commands from the folder the Puppet run is being executed from. If the brew user doesn't have enough permissions on that folder brew it will fail with an error not related to this.

We need to give a better error output to help the user run Puppet from a folder accessible by the brew user or try and run all brew commands from /tmp or similar "public" folder.

This is related to #100