https://golang.org/issue/33157 explains the issues with overlays. The
gopls tests caught this bug, but the go/packages tests didn't, so modify
the go/packages tests correspondingly.
Change-Id: I8ea8e06e145aa2420655cbe4884e60f36acfad7b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/186299
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>