Pass -find whenever possible to speed up go list calls. Add an
environment variable, GOPACKAGESDEBUG, that controls debug logging
so that we don't have to tell users to recompile goimports to debug it.
Change-Id: If39ff7829279dafa4e066e74a024c27a8235154b
Reviewed-on: https://go-review.googlesource.com/c/155477
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>