cmd/go: convert TestGoTestImportErrorStack to the script framework

The literal string match had to be turned into a regexp, otherwise
pretty straightforward.

Part of converting all tests to script framework to improve
test parallelism.

Updates #36320
Updates #17751

Change-Id: I46f62312f02dc9adf83ed91c6f807420d29fbb12
Reviewed-on: https://go-review.googlesource.com/c/go/+/212939


Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>