Allow password policy minlength to be removed like other values
    
    This is a side-effect of adding the libpwquality options. It
    imposes its own hardcoded minimum password length so some care
    was needed to ensure that it isn't set too low.
    
    So if there are no libpwquality options used then it's fine to
    have no minlength in the policy.
    
    Fixes: https://pagure.io/freeipa/issue/9297
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>