Get list of service from LDAP only at startup
    
    We check (possibly different) data from LDAP only at (re)start.
    This way we always shutdown exactly the services we started even if the list
    changed in the meanwhile (we avoid leaving a service running even if it was
    removed from LDAP as the admin decided it should not be started in future).
    
    This should also fix a problematic deadlock with systemd when we try to read
    the list of service from LDAP at shutdown.