Call 'dns_zone_rekey' after a 'rndc dnssec -checkds' or 'rndc dnssec
-rollover' command is received, because such a command may influence
the next key event. Updating the keys immediately avoids unnecessary
rollover delays.
The kasp system test no longer needs to call 'rndc loadkeys' after
a 'rndc dnssec -checkds' or 'rndc dnssec -rollover' command.