The test requires that timerproc runs, but busy loops and starves
the scheduler so that, with high probability, timerproc doesn't run.
Avoid the issue by expecting the test to succeed; if not, a major
outside timeout will kill it and let us know.

As you can see from the diffs, there have been several attempts to
fix this with chicanery, but none has worked. Don't bother trying
any more.

Fixes #8136.

LGTM=rsc
R=rsc, josharian
CC=golang-codereviews
https://golang.org/cl/105140043