[FIX] tools: export translations of models.py

When exporting the translations, the terms stored in individual files outside of
addons folders (e.g. openerp/models.py) needs to be scanned as well and added in
base translations.
Some folders like osv and report were enough to add these files but with the new
api moving the ORM to openerp folder, a non-recusrive scan needs to be added.

Fixes #7482