Scripts/openchange_user_cleanup: Don't hardcode samba private dir, use samba LoadParm()

Signed-off-by: Kamen Mazdrashki <kmazdrashki@zentyal.com>
Merge pull request #24 from Zentyal/kamenim/master-fix-7768

Scripts/openchange_user_cleanup: Don't hardcode samba private dir, use samba LoadParm()