Added an option to manage the files in the work dir

Hello and thanks for your module, in my environment I found puppet agent to hung while eating a lot of memory .

With a strace i discovered that it was reading all my nexus_work directory (that contains around 200K files) and this was "killing" the puppet agent run.

So I've added an option ( nexus_work_recurse) to be able to choose to manage recursively all the files in the work dir, on systems with a lot of files probably you want this to false, I've left the default to true, so it should be fully compatible with the past.