cmd/go: convert TestRunInternal to the script test framework

This conversion is a bit weird, because the original test runs in the cmd/go
directory, while the script test runs in the GOPATH directory. So even though
it's not necessary for the new test, it changes dircectory to $WORK, so that
its error message regexp can have four components like the original, just
changing the old gopath directory 'testdata' the new one 'gopath'.

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

Updates #36320
Updates #17751

Change-Id: Ie5b029c43dc22167278d3104b37c0b57c61326be
Reviewed-on: https://go-review.googlesource.com/c/go/+/212814


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