cmd/buildlet/stage0: move some logging around for the Windows untar mode
cmd/buildlet/stage0: move some logging around for the Windows untar mode

Change-Id: I7f5048b6f8e1806cb7801bf903a943eb503b2fc4
Reviewed-on: https://go-review.googlesource.com/51191
Reviewed-by: Jeff Johnson <e0aeede46a59107c4d834f64851ee491686571e7@google.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build