cmd/go: 3 cmd/go tests (>8s) made as non-short scripts

* TestAtomicCoverpkgAll -> Script/cover_atomic_pkgall.txt and make it
* non-short
* TestCoverpkgAllRuntime -> Script/cover_pkgall_runtime.txt and make it
* non-short
* TestCpuprofileTwice -> Script/cpu_profile_twice.txt and make it
* non-short
* TestGoTestMainTwice -> make it non-short

Updates #26472

Change-Id: I24f3d4c2a8b6e317adb369a1b1426e693f9571ed
Reviewed-on: https://go-review.googlesource.com/126636


Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>