Do not wait on std{out,err} when a test times out.

Do not wait on std{out,err} when a test times out.

The test wrapper currently waits on each of the process, stdout copy,
and stderr copy in turn. This makes it difficult to determine whether
or not the test did in fact time out, as the time in which it may
write to its output streams is effectively twice or thrice the
time used to determine success or failure (i.e. the process wait
timeout). This can cause situations like what we've seen in dotnet/coreclr#10076,
where the harness reports that the process timed out but the test's
output indicates a successful run.

This change only waits on stdout/stderr if the process completes within
the time allotted; otherwise it cancels the copies and promptly reports
the timeout.

Commit migrated from https://github.com/dotnet/coreclr/commit/bd7a88958776655867a4af3184dfef317f33839d