Copy the execopts of stress to stress.numthr

These two test are supposed to be the same and the variations exist because we
don't have a way to specify a different execenv for one test. Without this
change stress.numthr was segfaulting with qthreads because it was trying to
create way too many threads at once. This test didn't segfault for fifo because
only so many tasks (pthreads) could be created at once so the system didn't run
out of memory. With qthreads places no limit and thus with too many tasks at
once we run out of memory and segfault.