cmd/buildlet/stage0, env/windows: wait for network, don't expire passwords

Also, I rebuilt the Windows image with the 30GB base image. I named it
-v2 during manual testing with gomote, and I'm keeping it like that
now, so update dashboard/builders.go too.

Fixes golang/go#10071

Change-Id: I30029310cbf61fb21ef80063f9822cb90ce843c0
Reviewed-on: https://go-review.googlesource.com/7914
Reviewed-by: David Crawshaw <crawshaw@golang.org>
4 files changed