cmd/go/internal/script: use the Cancel and WaitDelay fields for subprocesses
The Cancel and WaitDelay fields recently added to exec.Cmd are
intended to support exactly the sort of cancellation behavior that we
need for script tests. Use them, and simplify the cmd/go tests
accordingly.
The more robust implementation may also help to diagose recurring test
hangs (#50187).
For #50187.
Updates #27494.
Change-Id: I7817fca0dd9a18e18984a252d3116f6a5275a401
Reviewed-on: https://go-review.googlesource.com/c/go/+/445357
Run-TryBot: Bryan Mills <bcmills@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>