It uses low level thread::wait_until() now which calls caller supplied
predicate with preemption disabled. If caller supplied code access not yet
mapped memory it will trigger an assertion on a page fault path.

Reviewed-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Gleb Natapov <gleb@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>