Further tweaking of deadlock isolation tests.

Further tweaking of deadlock isolation tests.

The new deadlock-soft-2 test has a timing dependency too: it supposes
that isolationtester will detect step s1b as waiting before the deadlock
detector runs and grants it the lock.  Adjust deadlock_timeout to ensure
that that's true even in CLOBBER_CACHE_ALWAYS builds, where the wait
detection query is quite slow.  Per buildfarm member jaguarundi.