Add code to be able to set default kinit lifetime
    
    This is done by setting the kinit_lifetime option in default.conf
    to a value that can be passed in with the -l option syntax of kinit.
    
    https://pagure.io/freeipa/issue/7001
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-By: Pavel Vomacka <pvomacka@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>