extend rndc timeout to 60 seconds

extend rndc timeout to 60 seconds

the idle timeout for rndc connections was set to 10 seconds, but this
caused intermittent system failures of the 'rndc' system test on slow
platforms, since 'rndc reconfig' could time out before reconfiguration
was complete.

this commit restores the original timeout value of 60 seconds, which was
changed inadvertently after rndc was updated to use the network manager.

even with this change, however, the test can still time out under
TSAN because loading the huge zone can take a very long time (upwards
of two minutes). so the test is modified here to generate a smaller zone
file when running under TSAN.