LDAP import: Group ID may be in `cn` or `fullname` attribute - deal with it

LDAP synchronization failed at group ids.
@phgross pached that in the egg. Please move the fix to opengever.core.

```
# Group name is in the 'cn' attribute, which is mapped to 'fullname'
            # XXX PATHCHED
            info['groupid'] = info.get('cn')[0]
            info['groupid'] = info['groupid'].decode('utf-8')
```
https://github.com/4teamwork/opengever.core/blob/master/opengever/ogds/base/ldap_import/ogds_updater.py#L127