The bash version of the test wrote intermediate files to its testdata directory.

Updates #28387
Updates #30316
Fixes #35536

Change-Id: Ib81b547d3c43e90df713a2172c8f399fefb53c68
Reviewed-on: https://go-review.googlesource.com/c/go/+/206901
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>