Limit pwpolicy maxlife to 20000 days
    
    Since krbMaxPwdLife attribute is represented as number of seconds,
    setting maxlife to high values such as 999 999 days (~2739 years)
    would result to overflow when parsing this attribute in kdb plugin,
    and hence default maxlife of 90 days would be applied.
    
    Limit the maximum value of maxlife that can be set through the
    framework to 20 000 days (~ 54 years).
    
    https://fedorahosted.org/freeipa/ticket/3817