naggen2: read config from puppet.conf

As namespace clashes made it difficult to fetch data from the puppet
class, I decided to follow advice I got on the previous change and read
directly from puppet.conf.

Change-Id: I4e0bac3b93a2bfdcc49c7b3bd8b588af8bac3374
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>