DRTVWR-476: Use a longer default timeout for Sync class.

The timeout is meant to prevent a deadlocked test program from hanging a
build. It's not intended to ensure some sort of SLA for the operations under
test. Empirically, using a longer timeout helps some test programs. The only
downside of increasing the timeout is that if some test does hang, it takes
longer to notice. But changes on the order of a few seconds are negligible.