Make the list of users that can skip passwrod policies configurable.
    Addresses bz#471130
    
    Also fix bugs in ipapwd_start.
    Also remove mutex, it is not necessary with the current code,
    we needed it when we used to change reload the configuration and
    keep it referenced in a static pointer.
    ipapwd_start runs only once and the global variables it sets are fixed
    in stone until DS is restarted.