[FIX] models.py: log the full traceback when record import fails

Without the full stack trace, it is very hard for the developers to know
why and where the record creation has failed.

closes odoo/odoo#29143

odoo/models.py

@@ -893,6 +893,7 @@ class BaseModel(object):
                 # avoid broken transaction) and keep going
                 cr.execute('ROLLBACK TO SAVEPOINT model_load_save')
             except Exception as e:
+                _logger.exception("Error while loading record")
                 message = (_('Unknown error during import:') + ' %s: %s' % (type(e), unicode(e.message or e.name)))
                 moreinfo = _('Resolve other errors first')
                 messages.append(dict(info, type='error', message=message, moreinfo=moreinfo))