all: rename vendored golang.org/x/net packages to golang_org

all: rename vendored golang.org/x/net packages to golang_org

Regression from Go 1.6 to Go 1.7rc1: we had broken the ability for
users to vendor "golang.org/x/net/http2" or "golang.org/x/net/route"
because we were vendoring them ourselves and cmd/go and cmd/compile do
not understand multiple vendor directories across multiple GOPATH
workspaces (e.g. user's $GOPATH and default $GOROOT).

As a short-term fix, since fixing cmd/go and cmd/compile is too
invasive at this point in the cycle, just rename "golang.org" to
"golang_org" for the standard library's vendored copy.

Fixes #16333

Change-Id: I9bfaed91e9f7d4ca6bab07befe80d71d437a21af
Reviewed-on: https://go-review.googlesource.com/24902
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>