sem_clockwait_np test: relax time constraint on VMs

In a guest on a busy hypervisor, the time remaining after an
interrupted sleep could be much lower than other environments.
Relax the lower bound on VMs.

MFC after: 1 week
Sponsored by: Dell EMC Isilon

(cherry picked from commit 31466594cd09d1413dbd8cab516fafc3557c2200)