Implement new -T options for xfer system tests

Implement new -T options for xfer system tests

'-T transferinsecs' makes named interpret the max-transfer-time-out,
max-transfer-idle-out, max-transfer-time-in and max-transfer-idle-in
configuration options as seconds instead of minutes.

'-T transferslowly' makes named to sleep for one second for every
xfrout message.

'-T transferstuck' makes named to sleep for one minute for every
xfrout message.