[dev.fuzz] testing: F.Setenv plus various fixes and revisions
I spent some time looking through all the changes we've made to
testing and cmd/go/... on the dev.fuzz branch. CL 348469 shows those
differences. This CL fixes comments, TODOs, and simplifies code in a
few places. It also implements F.Setenv.
Change-Id: I6fd7ef5fbd0bb6055e38d56cb42bddcf6f4ffdaf
Reviewed-on: https://go-review.googlesource.com/c/go/+/349109
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Katie Hockman <katie@golang.org>