cmd/buildlet/stage0: fix vet formatting warnings
cmd/buildlet/stage0: fix vet formatting warnings

Change-Id: I632036f04924b0b1d2211bda1dd7741f3cf225e1
Reviewed-on: https://go-review.googlesource.com/128635
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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