This CL also changes windows LookupSRV to return
_xmpp-server._tcp.google.com. as cname instead of google.com
similar to linux. Otherwise TestLookupDots still fails.

Updates #12193 (with plan9 still to do)

Change-Id: Id225e15bee95037cdb4226803506cce690c5d341
Reviewed-on: https://go-review.googlesource.com/13887
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>